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Provide support to increase developer productivity in Java when using MongoDB. Uses familiar Spring concepts such as a template classes for core API usage and lightweight repository style data access.
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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
<chapter id="mongo.core">
<title>MongoDB support</title>
<para>The MongoDB support contains a wide range of features which are
summarized below.</para>
<itemizedlist>
<listitem>
<para>Spring configuration support using Java based @Configuration
classes or an XML namespace for a Mongo driver instance and replica
sets</para>
</listitem>
<listitem>
<para>MongoTemplate helper class that increases productivity performing
common Mongo operations. Includes integrated object mapping between
documents and POJOs.</para>
</listitem>
<listitem>
<para>Exception translation into Spring's portable Data Access Exception
hierarchy</para>
</listitem>
<listitem>
<para>Feature Rich Object Mapping integrated with Spring's Conversion
Service</para>
</listitem>
<listitem>
<para>Annotation based mapping metadata but extensible to support other
metadata formats</para>
</listitem>
<listitem>
<para>Persistence and mapping lifecycle events</para>
</listitem>
<listitem>
<para>Java based Query, Criteria, and Update DSLs</para>
</listitem>
<listitem>
<para>Automatic implementation of Repository interfaces including
support for custom finder methods.</para>
</listitem>
<listitem>
<para>QueryDSL integration to support type-safe queries.</para>
</listitem>
<listitem>
<para>Cross-store persistance - support for JPA Entities with fields
transparently persisted/retrieved using MongoDB</para>
</listitem>
<listitem>
<para>Log4j log appender</para>
</listitem>
<listitem>
<para>GeoSpatial integration</para>
</listitem>
</itemizedlist>
<para>For most tasks you will find yourself using
<classname>MongoTemplate</classname> or the Repository support that both
leverage the rich mapping functionality. MongoTemplate is the place to look
for accessing functionality such as incrementing counters or ad-hoc CRUD
operations. MongoTemplate also provides callback methods so that it is easy
for you to get a hold of the low level API artifacts such as
<literal>org.mongo.DB</literal> to communicate directly with MongoDB. The
goal with naming conventions on various API artifacts is to copy those in
the base MongoDB Java driver so you can easily map your existing knowledge
onto the Spring APIs.</para>
<section id="mongodb-getting-started">
<title>Getting Started</title>
<para>Spring MongoDB support requires MongoDB 1.4 or higher and Java SE 5
or higher. The latest production release (2.4.9 as of this writing) is
recommended. An easy way to bootstrap setting up a working environment is
to create a Spring based project in <ulink
url="http://spring.io/tools/sts">STS</ulink>.</para>
<para>First you need to set up a running Mongodb server. Refer to the
<ulink url="http://docs.mongodb.org/manual/core/introduction/">Mongodb
Quick Start guide</ulink> for an explanation on how to startup a MongoDB
instance. Once installed starting MongoDB is typically a matter of
executing the following command:
<literal>MONGO_HOME/bin/mongod</literal></para>
<para>To create a Spring project in STS go to File -&gt; New -&gt; Spring
Template Project -&gt; Simple Spring Utility Project -&gt; press Yes when
prompted. Then enter a project and a package name such as
org.spring.mongodb.example.</para>
<para>Then add the following to pom.xml dependencies section.</para>
<programlisting lang="" language="xml">&lt;dependencies&gt;
&lt;!-- other dependency elements omitted --&gt;
&lt;dependency&gt;
&lt;groupId&gt;org.springframework.data&lt;/groupId&gt;
&lt;artifactId&gt;spring-data-mongodb&lt;/artifactId&gt;
&lt;version&gt;1.4.2.RELEASE&lt;/version&gt;
&lt;/dependency&gt;
&lt;/dependencies&gt;</programlisting>
<para>Also change the version of Spring in the pom.xml to be</para>
<programlisting lang="" language="xml">&lt;spring.framework.version&gt;3.2.8.RELEASE&lt;/spring.framework.version&gt;</programlisting>
<para>You will also need to add the location of the Spring Milestone
repository for maven to your pom.xml which is at the same level of your
&lt;dependencies/&gt; element</para>
<programlisting language="xml">&lt;repositories&gt;
&lt;repository&gt;
&lt;id&gt;spring-milestone&lt;/id&gt;
&lt;name&gt;Spring Maven MILESTONE Repository&lt;/name&gt;
&lt;url&gt;http://repo.spring.io/libs-milestone&lt;/url&gt;
&lt;/repository&gt;
&lt;/repositories&gt;</programlisting>
<para>The repository is also <ulink
url="http://shrub.appspot.com/maven.springframework.org/milestone/org/springframework/data/">browseable
here</ulink>.</para>
<para>You may also want to set the logging level to <code>DEBUG</code> to
see some additional information, edit the log4j.properties file to
have</para>
<programlisting>log4j.category.org.springframework.data.document.mongodb=DEBUG
log4j.appender.stdout.layout.ConversionPattern=%d{ABSOLUTE} %5p %40.40c:%4L - %m%n</programlisting>
<para>Create a simple Person class to persist</para>
<programlisting language="java">package org.spring.mongodb.example;
public class Person {
private String id;
private String name;
private int age;
public Person(String name, int age) {
this.name = name;
this.age = age;
}
public String getId() {
return id;
}
public String getName() {
return name;
}
public int getAge() {
return age;
}
@Override
public String toString() {
return "Person [id=" + id + ", name=" + name + ", age=" + age + "]";
}
}</programlisting>
<para>And a main application to run</para>
<programlisting language="java">package org.spring.mongodb.example;
import static org.springframework.data.mongodb.core.query.Criteria.where;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.data.mongodb.core.MongoOperations;
import org.springframework.data.mongodb.core.MongoTemplate;
import org.springframework.data.mongodb.core.query.Query;
import com.mongodb.Mongo;
public class MongoApp {
private static final Log log = LogFactory.getLog(MongoApp.class);
public static void main(String[] args) throws Exception {
MongoOperations mongoOps = new MongoTemplate(new Mongo(), "database");
mongoOps.insert(new Person("Joe", 34));
log.info(mongoOps.findOne(new Query(where("name").is("Joe")), Person.class));
mongoOps.dropCollection("person");
}
}</programlisting>
<para>This will produce the following output</para>
<programlisting>10:01:32,062 DEBUG apping.MongoPersistentEntityIndexCreator: 80 - Analyzing class class org.spring.example.Person for index information.
10:01:32,265 DEBUG ramework.data.mongodb.core.MongoTemplate: 631 - insert DBObject containing fields: [_class, age, name] in collection: Person
10:01:32,765 DEBUG ramework.data.mongodb.core.MongoTemplate:1243 - findOne using query: { "name" : "Joe"} in db.collection: database.Person
10:01:32,953 INFO org.spring.mongodb.example.MongoApp: 25 - Person [id=4ddbba3c0be56b7e1b210166, name=Joe, age=34]
10:01:32,984 DEBUG ramework.data.mongodb.core.MongoTemplate: 375 - Dropped collection [database.person]</programlisting>
<para>Even in this simple example, there are few things to take notice
of</para>
<itemizedlist>
<listitem>
<para>You can instantiate the central helper class of Spring Mongo,
<link
linkend="mongo-template"><classname>MongoTemplate</classname></link>,
using the standard <classname>com.mongodb.Mongo</classname> object and
the name of the database to use.</para>
</listitem>
<listitem>
<para>The mapper works against standard POJO objects without the need
for any additional metadata (though you can optionally provide that
information. See <link linkend="mongo.mapping">here</link>.).</para>
</listitem>
<listitem>
<para>Conventions are used for handling the id field, converting it to
be a ObjectId when stored in the database.</para>
</listitem>
<listitem>
<para>Mapping conventions can use field access. Notice the Person
class has only getters.</para>
</listitem>
<listitem>
<para>If the constructor argument names match the field names of the
stored document, they will be used to instantiate the object</para>
</listitem>
</itemizedlist>
</section>
<section id="mongo.examples-repo">
<title>Examples Repository</title>
<para>There is an <ulink
url="https://github.com/spring-projects/spring-data-document-examples">github
repository with several examples</ulink> that you can download and play
around with to get a feel for how the library works.</para>
</section>
<section id="mongodb-connectors">
<title>Connecting to MongoDB with Spring</title>
<para>One of the first tasks when using MongoDB and Spring is to create a
<classname>com.mongodb.Mongo</classname> object using the IoC container.
There are two main ways to do this, either using Java based bean metadata
or XML based bean metadata. These are discussed in the following sections.
<note>
<para>For those not familiar with how to configure the Spring
container using Java based bean metadata instead of XML based metadata
see the high level introduction in the reference docs <ulink
url="http://docs.spring.io/spring/docs/3.2.x/spring-framework-reference/html/new-in-3.0.html#new-java-configuration"
userlevel="">here </ulink> as well as the detailed documentation<ulink
url="http://docs.spring.io/spring/docs/3.2.x/spring-framework-reference/html/beans.html#beans-java-instantiating-container">
here</ulink>.</para>
</note></para>
<section id="mongo.mongo-java-config">
<title>Registering a Mongo instance using Java based metadata</title>
<para>An example of using Java based bean metadata to register an
instance of a <classname>com.mongodb.Mongo</classname> is shown below
<example>
<title>Registering a com.mongodb.Mongo object using Java based bean
metadata</title>
<programlisting language="java">@Configuration
public class AppConfig {
/*
* Use the standard Mongo driver API to create a com.mongodb.Mongo instance.
*/
public @Bean Mongo mongo() throws UnknownHostException {
return new Mongo("localhost");
}
} </programlisting>
</example></para>
<para>This approach allows you to use the standard
<classname>com.mongodb.Mongo</classname> API that you may already be
used to using but also pollutes the code with the UnknownHostException
checked exception. The use of the checked exception is not desirable as
Java based bean metadata uses methods as a means to set object
dependencies, making the calling code cluttered.</para>
<para>An alternative is to register an instance of
<classname>com.mongodb.Mongo</classname> instance with the container
using Spring's<interfacename> MongoFactoryBean</interfacename>. As
compared to instantiating a <classname>com.mongodb.Mongo</classname>
instance directly, the FactoryBean approach does not throw a checked
exception and has the added advantage of also providing the container
with an ExceptionTranslator implementation that translates MongoDB
exceptions to exceptions in Spring's portable
<classname>DataAccessException</classname> hierarchy for data access
classes annoated with the <literal>@Repository</literal> annotation.
This hierarchy and use of <literal>@Repository</literal> is described in
<ulink
url="http://docs.spring.io/spring/docs/current/spring-framework-reference/html/dao.html">Spring's
DAO support features</ulink>.</para>
<para>An example of a Java based bean metadata that supports exception
translation on <classname>@Repository</classname> annotated classes is
shown below:</para>
<example>
<title>Registering a com.mongodb.Mongo object using Spring's
MongoFactoryBean and enabling Spring's exception translation
support</title>
<programlisting language="java">@Configuration
public class AppConfig {
/*
* Factory bean that creates the com.mongodb.Mongo instance
*/
public @Bean MongoFactoryBean mongo() {
MongoFactoryBean mongo = new MongoFactoryBean();
mongo.setHost("localhost");
return mongo;
}
}
</programlisting>
<para>To access the <classname>com.mongodb.Mongo</classname> object
created by the <classname>MongoFactoryBean</classname> in other
<literal>@Configuration</literal> or your own classes, use a
"<literal>private @Autowired Mongo mongo;</literal>" field.</para>
</example>
</section>
<section id="mongo.mongo-xml-config">
<title>Registering a Mongo instance using XML based metadata</title>
<para>While you can use Spring's traditional
<literal>&lt;beans/&gt;</literal> XML namespace to register an instance
of <classname>com.mongodb.Mongo</classname> with the container, the XML
can be quite verbose as it is general purpose. XML namespaces are a
better alternative to configuring commonly used objects such as the
Mongo instance. The mongo namespace alows you to create a Mongo instance
server location, replica-sets, and options.</para>
<para>To use the Mongo namespace elements you will need to reference the
Mongo schema:</para>
<example>
<title>XML schema to configure MongoDB</title>
<programlisting language="xml">&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:mongo="http://www.springframework.org/schema/data/mongo"
xsi:schemaLocation=
"http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.0.xsd
<emphasis role="bold">http://www.springframework.org/schema/data/mongo
http://www.springframework.org/schema/data/mongo/spring-mongo-1.0.xsd</emphasis>
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd"&gt;
&lt;!-- Default bean name is 'mongo' --&gt;
<emphasis role="bold">&lt;mongo:mongo host="localhost" port="27017"/&gt;</emphasis>
&lt;/beans&gt;
</programlisting>
</example>
<para>A more advanced configuration with MongoOptions is shown below
(note these are not recommended values)</para>
<example>
<title>XML schema to configure a com.mongodb.Mongo object with
MongoOptions</title>
<programlisting language="xml">&lt;beans&gt;
&lt;mongo:mongo host="localhost" port="27017"&gt;
&lt;mongo:options connections-per-host="8"
threads-allowed-to-block-for-connection-multiplier="4"
connect-timeout="1000"
max-wait-time="1500}"
auto-connect-retry="true"
socket-keep-alive="true"
socket-timeout="1500"
slave-ok="true"
write-number="1"
write-timeout="0"
write-fsync="true"/&gt;
&lt;/mongo:mongo/&gt;
&lt;/beans&gt;
</programlisting>
</example>
<para>A configuration using replica sets is shown below. <example>
<title>XML schema to configure com.mongodb.Mongo object with Replica
Sets</title>
<programlisting language="xml">&lt;mongo:mongo id="replicaSetMongo" replica-set="127.0.0.1:27017,localhost:27018"/&gt; </programlisting>
</example></para>
</section>
<section id="mongo.mongo-db-factory">
<title>The MongoDbFactory interface</title>
<para>While <classname>com.mongodb.Mongo</classname> is the entry point
to the MongoDB driver API, connecting to a specific MongoDB database
instance requires additional information such as the database name and
an optional username and password. With that information you can obtain
a com.mongodb.DB object and access all the functionality of a specific
MongoDB database instance. Spring provides the
<classname>org.springframework.data.mongodb.core.MongoDbFactory</classname>
interface shown below to bootstrap connectivity to the database.</para>
<programlisting language="java">public interface MongoDbFactory {
DB getDb() throws DataAccessException;
DB getDb(String dbName) throws DataAccessException;
}</programlisting>
<para>The following sections show how you can use the container with
either Java or the XML based metadata to configure an instance of the
<classname>MongoDbFactory</classname> interface. In turn, you can use
the <classname>MongoDbFactory</classname> instance to configure
MongoTemplate.</para>
<para>The class
<classname>org.springframework.data.mongodb.core.SimpleMongoDbFactory</classname>
provides implements the MongoDbFactory interface and is created with a
standard <classname>com.mongodb.Mongo</classname> instance, the database
name and an optional
<classname>org.springframework.data.authentication.UserCredentials</classname>
constructor argument.</para>
<para>Instead of using the IoC container to create an instance of
MongoTemplate, you can just use them in standard Java code as shown
below.</para>
<programlisting language="java">public class MongoApp {
private static final Log log = LogFactory.getLog(MongoApp.class);
public static void main(String[] args) throws Exception {
MongoOperations mongoOps = new MongoTemplate(<emphasis role="bold">new SimpleMongoDbFactory(new Mongo(), "database")</emphasis>);
mongoOps.insert(new Person("Joe", 34));
log.info(mongoOps.findOne(new Query(where("name").is("Joe")), Person.class));
mongoOps.dropCollection("person");
}
}</programlisting>
<para>The code in bold highlights the use of SimpleMongoDbFactory and is
the only difference between the listing shown in the <link lang=""
linkend="mongodb-getting-started" os="">getting started
section</link>.</para>
</section>
<section id="mongo.mongo-db-factory-java">
<title>Registering a MongoDbFactory instance using Java based
metadata</title>
<para>To register a MongoDbFactory instance with the container, you
write code much like what was highlighted in the previous code listing.
A simple example is shown below</para>
<programlisting language="java">@Configuration
public class MongoConfiguration {
public @Bean MongoDbFactory mongoDbFactory() throws Exception {
return new SimpleMongoDbFactory(new Mongo(), "database");
}
}</programlisting>
<para>To define the username and password create an instance of
<classname>org.springframework.data.authentication.UserCredentials</classname>
and pass it into the constructor as shown below. This listing also shows
using <classname>MongoDbFactory</classname> register an instance of
MongoTemplate with the container.</para>
<programlisting language="java">@Configuration
public class MongoConfiguration {
public @Bean MongoDbFactory mongoDbFactory() throws Exception {
UserCredentials userCredentials = new UserCredentials("joe", "secret");
return new SimpleMongoDbFactory(new Mongo(), "database", userCredentials);
}
public @Bean MongoTemplate mongoTemplate() throws Exception {
return new MongoTemplate(mongoDbFactory());
}
}</programlisting>
</section>
<section id="mongo.mongo-db-factory-xml">
<title>Registering a MongoDbFactory instance using XML based
metadata</title>
<para>The mongo namespace provides a convient way to create a
<classname>SimpleMongoDbFactory</classname> as compared to using
the<literal>&lt;beans/&gt;</literal> namespace. Simple usage is shown
below</para>
<programlisting language="xml">&lt;mongo:db-factory dbname="database"&gt;</programlisting>
<para>In the above example a <classname>com.mongodb.Mongo</classname>
instance is created using the default host and port number. The
<classname>SimpleMongoDbFactory</classname> registered with the
container is identified by the id 'mongoDbFactory' unless a value for
the id attribute is specified.</para>
<para>You can also provide the host and port for the underlying
<classname>com.mongodb.Mongo</classname> instance as shown below, in
addition to username and password for the database.</para>
<programlisting language="xml">&lt;mongo:db-factory id="anotherMongoDbFactory"
host="localhost"
port="27017"
dbname="database"
username="joe"
password="secret"/&gt;</programlisting>
<para>If you need to configure additional options on the
<classname>com.mongodb.Mongo</classname> instance that is used to create
a <classname>SimpleMongoDbFactory</classname> you can refer to an
existing bean using the <literal>mongo-ref</literal> attribute as shown
below. To show another common usage pattern, this listing show the use
of a property placeholder to parameterise the configuration and creating
<classname>MongoTemplate</classname>.</para>
<programlisting language="xml">&lt;context:property-placeholder location="classpath:/com/myapp/mongodb/config/mongo.properties"/&gt;
&lt;mongo:mongo host="${mongo.host}" port="${mongo.port}"&gt;
&lt;mongo:options
connections-per-host="${mongo.connectionsPerHost}"
threads-allowed-to-block-for-connection-multiplier="${mongo.threadsAllowedToBlockForConnectionMultiplier}"
connect-timeout="${mongo.connectTimeout}"
max-wait-time="${mongo.maxWaitTime}"
auto-connect-retry="${mongo.autoConnectRetry}"
socket-keep-alive="${mongo.socketKeepAlive}"
socket-timeout="${mongo.socketTimeout}"
slave-ok="${mongo.slaveOk}"
write-number="1"
write-timeout="0"
write-fsync="true"/&gt;
&lt;/mongo:mongo&gt;
&lt;mongo:db-factory dbname="database" mongo-ref="mongo"/&gt;
&lt;bean id="anotherMongoTemplate" class="org.springframework.data.mongodb.core.MongoTemplate"&gt;
&lt;constructor-arg name="mongoDbFactory" ref="mongoDbFactory"/&gt;
&lt;/bean&gt;</programlisting>
</section>
</section>
<section id="mongo.auditing">
<title>General auditing configuration</title>
<para>Activating auditing functionality is just a matter of adding the
Spring Data Mongo <literal>auditing</literal> namespace element to your
configuration:</para>
<example>
<title>Activating auditing using XML configuration</title>
<programlisting language="xml">&lt;mongo:auditing mapping-context-ref="customMappingContext" auditor-aware-ref="yourAuditorAwareImpl"/&gt;</programlisting>
</example>
<para>Since Spring Data MongoDB 1.4 auditing can be enabled by annotating
a configuration class with the <classname>@EnableMongoAuditing</classname>
annotation.</para>
<example>
<title>Activating auditing using JavaConfig</title>
<programlisting language="java">@Configuration
@EnableMongoAuditing
class Config {
@Bean
public AuditorAware&lt;AuditableUser&gt; myAuditorProvider() {
return new AuditorAwareImpl();
}
}</programlisting>
</example>
<para>If you expose a bean of type
<interfacename>AuditorAware</interfacename> to the
<interfacename>ApplicationContext</interfacename>, the auditing
infrastructure will pick it up automatically and use it to determine the
current user to be set on domain types. If you have multiple
implementations registered in the
<interfacename>ApplicationContext</interfacename>, you can select the one
to be used by explicitly setting the <code>auditorAwareRef</code>
attribute of <interfacename>@EnableJpaAuditing</interfacename>.</para>
</section>
<section id="mongo-template">
<title>Introduction to MongoTemplate</title>
<para>The class <classname>MongoTemplate</classname>, located in the
package <literal>org.springframework.data.document.mongodb</literal>, is
the central class of the Spring's MongoDB support providng a rich feature
set to interact with the database. The template offers convenience
operations to create, update, delete and query for MongoDB documents and
provides a mapping between your domain objects and MongoDB
documents.</para>
<note>
<para>Once configured, <classname>MongoTemplate</classname> is
thread-safe and can be reused across multiple instances.</para>
</note>
<para>The mapping between MongoDB documents and domain classes is done by
delegating to an implementation of the interface
<interfacename>MongoConverter</interfacename>. Spring provides two
implementations, <classname>SimpleMappingConverter</classname> and
<classname>MongoMappingConverter</classname>, but you can also write your
own converter. Please refer to the section on MongoCoverters for more
detailed information.</para>
<para>The <classname>MongoTemplate</classname> class implements the
interface <interfacename>MongoOperations</interfacename>. In as much as
possible, the methods on <interfacename>MongoOperations</interfacename>
are named after methods available on the MongoDB driver
<classname>Collection</classname> object as as to make the API familiar to
existing MongoDB developers who are used to the driver API. For example,
you will find methods such as "find", "findAndModify", "findOne",
"insert", "remove", "save", "update" and "updateMulti". The design goal
was to make it as easy as possible to transition between the use of the
base MongoDB driver and <interfacename>MongoOperations</interfacename>. A
major difference in between the two APIs is that MongOperations can be
passed domain objects instead of <classname>DBObject</classname> and there
are fluent APIs for <classname>Query</classname>,
<classname>Criteria</classname>, and <classname>Update</classname>
operations instead of populating a <classname>DBObject</classname> to
specify the parameters for those operatiosn.</para>
<note>
<para>The preferred way to reference the operations on
<classname>MongoTemplate</classname> instance is via its interface
<interfacename>MongoOperations</interfacename>.</para>
</note>
<para>The default converter implementation used by
<classname>MongoTemplate</classname> is MongoMappingConverter. While the
<classname>MongoMappingConverter</classname> can make use of additional
metadata to specify the mapping of objects to documents it is also capable
of converting objects that contain no additonal metadata by using some
conventions for the mapping of IDs and collection names. These conventions
as well as the use of mapping annotations is explained in the <link
linkend="mongo.mapping">Mapping chapter</link>.<note>
<para>In the M2 release <classname>SimpleMappingConverter</classname>,
was the default and this class is now deprecated as its functionality
has been subsumed by the MongoMappingConverter.</para>
</note></para>
<para>Another central feature of MongoTemplate is exception translation of
exceptions thrown in the MongoDB Java driver into Spring's portable Data
Access Exception hierarchy. Refer to the section on <link
linkend="mongo.exception">exception translation</link> for more
information.</para>
<para>While there are many convenience methods on
<classname>MongoTemplate</classname> to help you easily perform common
tasks if you should need to access the MongoDB driver API directly to
access functionality not explicitly exposed by the MongoTemplate you can
use one of several Execute callback methods to access underlying driver
APIs. The execute callbacks will give you a reference to either a
<classname>com.mongodb.Collection</classname> or a
<classname>com.mongodb.DB</classname> object. Please see the section
<ulink url="mongo.executioncallback">Execution Callbacks</ulink> for more
information.</para>
<para>Now let's look at a examples of how to work with the
<classname>MongoTemplate</classname> in the context of the Spring
container.</para>
<section id="mongo-template.instantiating" label=" ">
<title>Instantiating MongoTemplate</title>
<para>You can use Java to create and register an instance of
MongoTemplate as shown below.</para>
<example>
<title>Registering a com.mongodb.Mongo object and enabling Spring's
exception translation support</title>
<programlisting language="java">@Configuration
public class AppConfig {
public @Bean Mongo mongo() throws Exception {
return new Mongo("localhost");
}
public @Bean MongoTemplate mongoTemplate() throws Exception {
return new MongoTemplate(mongo(), "mydatabase");
}
}
</programlisting>
</example>
<para>There are several overloaded constructors of MongoTemplate. These
are</para>
<itemizedlist>
<listitem>
<para><emphasis role="bold">MongoTemplate </emphasis>
<literal>(Mongo mongo, String databaseName)</literal> - takes the
<classname>com.mongodb.Mongo</classname> object and the default
database name to operate against.</para>
</listitem>
<listitem>
<para><emphasis role="bold">MongoTemplate </emphasis>
<literal>(Mongo mongo, String databaseName, UserCredentials
userCredentials) </literal> - adds the username and password for
authenticating with the database.</para>
</listitem>
<listitem>
<para><emphasis role="bold">MongoTemplate</emphasis>
<literal>(MongoDbFactory mongoDbFactory)</literal> - takes a
MongoDbFactory object that encapsulated the
<classname>com.mongodb.Mongo</classname> object, database name, and
username and password.</para>
</listitem>
<listitem>
<para><emphasis role="bold">MongoTemplate </emphasis>
<literal>(MongoDbFactory mongoDbFactory, MongoConverter
mongoConverter) </literal> - adds a MongoConverter to use for
mapping.</para>
</listitem>
</itemizedlist>
<para>You can also configure a MongoTemplate using Spring's XML
&lt;beans/&gt; schema.</para>
<programlisting language="java"> &lt;mongo:mongo host="localhost" port="27017"/&gt;
&lt;bean id="mongoTemplate" class="org.springframework.data.mongodb.core.MongoTemplate"&gt;
&lt;constructor-arg ref="mongo"/&gt;
&lt;constructor-arg name="databaseName" value="geospatial"/&gt;
&lt;/bean&gt;</programlisting>
<para>Other optional properties that you might like to set when creating
a <classname>MongoTemplate</classname> are the default
<classname>WriteResultCheckingPolicy</classname>,
<classname>WriteConcern</classname>, and
<classname>ReadPreference</classname>.</para>
<note>
<para>The preferred way to reference the operations on
<classname>MongoTemplate</classname> instance is via its interface
<interfacename>MongoOperations</interfacename>.</para>
</note>
<section id="mongo-template.writeresultchecking">
<title>WriteResultChecking Policy</title>
<para>When in development it is very handy to either log or throw an
exception if the <classname>com.mongodb.WriteResult</classname>
returned from any MongoDB operation contains an error. It is quite
common to forget to do this during development and then end up with an
application that looks like it runs successfully but in fact the
database was not modified according to your expectations. Set
MongoTemplate's <property>WriteResultChecking</property> property to
an enum with the following values, LOG, EXCEPTION, or NONE to either
log the error, throw and exception or do nothing. The default is to
use a <literal>WriteResultChecking</literal> value of NONE.</para>
</section>
<section id="mongo-template.writeconcern">
<title>WriteConcern</title>
<para>You can set the <classname>com.mongodb.WriteConcern</classname>
property that the <classname>MongoTemplate</classname> will use for
write operations if it has not yet been specified via the driver at a
higher level such as <classname>com.mongodb.Mongo</classname>. If
MongoTemplate's <classname>WriteConcern</classname> property is not
set it will default to the one set in the MongoDB driver's DB or
Collection setting.</para>
</section>
<section id="mongo-template.writeconcernresolver">
<title>WriteConcernResolver</title>
<para>For more advanced cases where you want to set different
<classname>WriteConcern</classname> values on a per-operation basis
(for remove, update, insert and save operations), a strategy interface
called <interfacename>WriteConcernResolver</interfacename> can be
configured on <classname>MongoTemplate</classname>. Since
<classname>MongoTemplate</classname> is used to persist POJOs, the
<interfacename>WriteConcernResolver</interfacename> lets you create a
policy that can map a specific POJO class to a
<classname>WriteConcern</classname> value. The
<interfacename>WriteConcernResolver</interfacename> interface is shown
below.</para>
<programlisting language="java">public interface WriteConcernResolver {
WriteConcern resolve(MongoAction action);
}</programlisting>
<para>The passed in argument, MongoAction, is what you use to
determine the <classname>WriteConcern</classname> value to be used or
to use the value of the Template itself as a default.
<classname>MongoAction</classname> contains the collection name being
written to, the <classname>java.lang.Class</classname> of the POJO,
the converted <classname>DBObject</classname>, as well as the
operation as an enumeration
(<classname>MongoActionOperation</classname>: REMOVE, UPDATE, INSERT,
INSERT_LIST, SAVE) and a few other pieces of contextual information.
For example,</para>
<programlisting>private class MyAppWriteConcernResolver implements WriteConcernResolver {
public WriteConcern resolve(MongoAction action) {
if (action.getEntityClass().getSimpleName().contains("Audit")) {
return WriteConcern.NONE;
} else if (action.getEntityClass().getSimpleName().contains("Metadata")) {
return WriteConcern.JOURNAL_SAFE;
}
return action.getDefaultWriteConcern();
}
}</programlisting>
</section>
</section>
</section>
<section id="mongo-template.save-update-remove">
<title>Saving, Updating, and Removing Documents</title>
<para><classname>MongoTemplate</classname> provides a simple way for you
to save, update, and delete your domain objects and map those objects to
documents stored in MongoDB.</para>
<para>Given a simple class such as Person</para>
<programlisting language="java">public class Person {
private String id;
private String name;
private int age;
public Person(String name, int age) {
this.name = name;
this.age = age;
}
public String getId() {
return id;
}
public String getName() {
return name;
}
public int getAge() {
return age;
}
@Override
public String toString() {
return "Person [id=" + id + ", name=" + name + ", age=" + age + "]";
}
}
</programlisting>
<para>You can save, update and delete the object as shown below.</para>
<note>
<para><interfacename>MongoOperations</interfacename> is the interface
that <classname>MongoTemplate</classname> implements.</para>
</note>
<programlisting language="java">package org.spring.example;
import static org.springframework.data.mongodb.core.query.Criteria.where;
import static org.springframework.data.mongodb.core.query.Update.update;
import static org.springframework.data.mongodb.core.query.Query.query;
import java.util.List;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.data.mongodb.core.MongoOperations;
import org.springframework.data.mongodb.core.MongoTemplate;
import org.springframework.data.mongodb.core.SimpleMongoDbFactory;
import com.mongodb.Mongo;
public class MongoApp {
private static final Log log = LogFactory.getLog(MongoApp.class);
public static void main(String[] args) throws Exception {
MongoOperations mongoOps = new MongoTemplate(new SimpleMongoDbFactory(new Mongo(), "database"));
Person p = new Person("Joe", 34);
// Insert is used to initially store the object into the database.
mongoOps.insert(p);
log.info("Insert: " + p);
// Find
p = mongoOps.findById(p.getId(), Person.class);
log.info("Found: " + p);
// Update
mongoOps.updateFirst(query(where("name").is("Joe")), update("age", 35), Person.class);
p = mongoOps.findOne(query(where("name").is("Joe")), Person.class);
log.info("Updated: " + p);
// Delete
mongoOps.remove(p);
// Check that deletion worked
List&lt;Person&gt; people = mongoOps.findAll(Person.class);
log.info("Number of people = : " + people.size());
mongoOps.dropCollection(Person.class);
}
}
</programlisting>
<para>This would produce the following log output (including debug
messages from <classname>MongoTemplate</classname> itself)</para>
<programlisting>DEBUG apping.MongoPersistentEntityIndexCreator: 80 - Analyzing class class org.spring.example.Person for index information.
DEBUG work.data.mongodb.core.MongoTemplate: 632 - insert DBObject containing fields: [_class, age, name] in collection: person
INFO org.spring.example.MongoApp: 30 - Insert: Person [id=4ddc6e784ce5b1eba3ceaf5c, name=Joe, age=34]
DEBUG work.data.mongodb.core.MongoTemplate:1246 - findOne using query: { "_id" : { "$oid" : "4ddc6e784ce5b1eba3ceaf5c"}} in db.collection: database.person
INFO org.spring.example.MongoApp: 34 - Found: Person [id=4ddc6e784ce5b1eba3ceaf5c, name=Joe, age=34]
DEBUG work.data.mongodb.core.MongoTemplate: 778 - calling update using query: { "name" : "Joe"} and update: { "$set" : { "age" : 35}} in collection: person
DEBUG work.data.mongodb.core.MongoTemplate:1246 - findOne using query: { "name" : "Joe"} in db.collection: database.person
INFO org.spring.example.MongoApp: 39 - Updated: Person [id=4ddc6e784ce5b1eba3ceaf5c, name=Joe, age=35]
DEBUG work.data.mongodb.core.MongoTemplate: 823 - remove using query: { "id" : "4ddc6e784ce5b1eba3ceaf5c"} in collection: person
INFO org.spring.example.MongoApp: 46 - Number of people = : 0
DEBUG work.data.mongodb.core.MongoTemplate: 376 - Dropped collection [database.person]</programlisting>
<para>There was implicit conversion using the
<interfacename>MongoConverter</interfacename> between a
<classname>String</classname> and <classname>ObjectId</classname> as
stored in the database and recognizing a convention of the property "Id"
name.</para>
<note>
<para>This example is meant to show the use of save, update and remove
operations on MongoTemplate and not to show complex mapping
functionality</para>
</note>
<para>The query syntax used in the example is explained in more detail in
the section <link linkend="mongo.query">Querying Documents</link>.</para>
<section id="mongo-template.id-handling">
<title>How the '_id' field is handled in the mapping layer</title>
<para>MongoDB requires that you have an '_id' field for all documents.
If you don't provide one the driver will assign a
<classname>ObjectId</classname> with a generated value. When using the
<classname>MongoMappingConverter</classname> there are certain rules
that govern how properties from the Java class is mapped to this '_id'
field.</para>
<para>The following outlines what property will be mapped to the '_id'
document field:</para>
<para><itemizedlist>
<listitem>
<para>A property or field annotated with
<classname>@Id</classname>
(<classname>org.springframework.data.annotation.Id</classname>)
will be mapped to the '_id' field.</para>
</listitem>
<listitem>
<para>A property or field without an annotation but named
<classname>id</classname> will be mapped to the '_id'
field.</para>
</listitem>
</itemizedlist></para>
<para>The following outlines what type conversion, if any, will be done
on the property mapped to the _id document field when using the
<classname>MappingMongoConverter</classname>, the default for
<classname>MongoTemplate</classname>.</para>
<itemizedlist>
<listitem>
<para>An id property or field declared as a String in the Java class
will be converted to and stored as an
<classname>ObjectId</classname> if possible using a Spring
<interfacename>Converter&lt;String, ObjectId&gt;</interfacename>.
Valid conversion rules are delegated to the MongoDB Java driver. If
it cannot be converted to an ObjectId, then the value will be stored
as a string in the database.</para>
</listitem>
<listitem>
<para>An id property or field declared as
<classname>BigInteger</classname> in the Java class will be
converted to and stored as an <classname>ObjectId</classname> using
a Spring <interfacename>Converter&lt;BigInteger,
ObjectId&gt;</interfacename>.</para>
</listitem>
</itemizedlist>
<para>If no field or property specified above is present in the Java
class then an implicit '_id' file will be generated by the driver but
not mapped to a property or field of the Java class.</para>
<para>When querying and updating <classname>MongoTemplate</classname>
will use the converter to handle conversions of the
<classname>Query</classname> and <classname>Update</classname> objects
that correspond to the above rules for saving documents so field names
and types used in your queries will be able to match what is in your
domain classes.</para>
</section>
<section id="mongo-template.type-mapping">
<title>Type mapping</title>
<para>As MongoDB collections can contain documents that represent
instances of a variety of types. A great example here is if you store a
hierarchy of classes or simply have a class with a property of type
<classname>Object</classname>. In the latter case the values held inside
that property have to be read in correctly when retrieving the object.
Thus we need a mechanism to store type information alongside the actual
document.</para>
<para>To achieve that the <classname>MappingMongoConverter</classname>
uses a <interfacename>MongoTypeMapper</interfacename> abstraction with
<classname>DefaultMongoTypeMapper</classname> as it's main
implementation. It's default behaviour is storing the fully qualified
classname under <code>_class</code> inside the document for the
top-level document as well as for every value if it's a complex type and
a subtype of the property type declared.</para>
<example>
<title>Type mapping</title>
<programlisting language="java">public class Sample {
Contact value;
}
public abstract class Contact { … }
public class Person extends Contact { … }
Sample sample = new Sample();
sample.value = new Person();
mongoTemplate.save(sample);
{ "_class" : "com.acme.Sample",
"value" : { "_class" : "com.acme.Person" }
}</programlisting>
</example>
<para>As you can see we store the type information for the actual root
class persistent as well as for the nested type as it is complex and a
subtype of <classname>Contact</classname>. So if you're now using
<methodname>mongoTemplate.findAll(Object.class, "sample")</methodname>
we are able to find out that the document stored shall be a
<classname>Sample</classname> instance. We are also able to find out
that the value property shall be a <classname>Person</classname>
actually.</para>
<simplesect>
<title>Customizing type mapping</title>
<para>In case you want to avoid writing the entire Java class name as
type information but rather like to use some key you can use the
<interfacename>@TypeAlias</interfacename> annotation at the entity
class being persisted. If you need to customize the mapping even more
have a look at the
<interfacename>TypeInformationMapper</interfacename> interface. An
instance of that interface can be configured at the
<classname>DefaultMongoTypeMapper</classname> which can be configured
in turn on <classname>MappingMongoConverter</classname>.</para>
<example>
<title>Defining a TypeAlias for an Entity</title>
<programlisting language="java">@TypeAlias("pers")
class Person {
}</programlisting>
<para>Note that the resulting document will contain
<code>"pers"</code> as the value in the <code>_class</code>
Field.</para>
</example>
</simplesect>
<simplesect>
<title>Configuring custom type mapping</title>
<para>The following example demonstrates how to configure a custom
<classname>MongoTypeMapper</classname> in
<classname>MappingMongoConverter</classname>.</para>
<example>
<title>Configuring a custom MongoTypeMapper via Spring Java
Config</title>
<programlisting language="java">class CustomMongoTypeMapper extends DefaultMongoTypeMapper {
//implement custom type mapping here
}</programlisting>
<programlisting language="java">@Configuration
class SampleMongoConfiguration extends AbstractMongoConfiguration {
@Override
protected String getDatabaseName() {
return "database";
}
@Override
public Mongo mongo() throws Exception {
return new Mongo();
}
@Bean
@Override
public MappingMongoConverter mappingMongoConverter() throws Exception {
MappingMongoConverter mmc = super.mappingMongoConverter();
mmc.setTypeMapper(customTypeMapper());
return mmc;
}
@Bean
public MongoTypeMapper customTypeMapper() {
return new CustomMongoTypeMapper();
}
}</programlisting>
<para>Note that we are extending the
<classname>AbstractMongoConfiguration</classname> class and override
the bean definition of the
<classname>MappingMongoConverter</classname> where we configure our
custom <classname>MongoTypeMapper</classname>.</para>
</example>
<example>
<title>Configuring a custom MongoTypeMapper via XML</title>
<programlisting language="xml">&lt;mongo:mapping-converter type-mapper-ref="customMongoTypeMapper"/&gt;
&lt;bean name="customMongoTypeMapper" class="com.bubu.mongo.CustomMongoTypeMapper"/&gt;</programlisting>
</example>
</simplesect>
</section>
<section id="mongo-template.save-insert">
<title>Methods for saving and inserting documents</title>
<para>There are several convenient methods on
<classname>MongoTemplate</classname> for saving and inserting your
objects. To have more fine grained control over the conversion process
you can register Spring converters with the
<classname>MappingMongoConverter</classname>, for example
<interfacename>Converter&lt;Person, DBObject&gt;</interfacename> and
<interfacename>Converter&lt;DBObject, Person&gt;</interfacename>.</para>
<note>
<para>The difference between insert and save operations is that a save
operation will perform an insert if the object is not already
present.</para>
</note>
<para>The simple case of using the save operation is to save a POJO. In
this case the collection name will be determined by name (not fully
qualfied) of the class. You may also call the save operation with a
specific collection name. The collection to store the object can be
overriden using mapping metadata.</para>
<para>When inserting or saving, if the Id property is not set, the
assumption is that its value will be auto-generated by the database. As
such, for auto-generation of an ObjectId to succeed the type of the Id
property/field in your class must be either a
<classname>String</classname>, <classname>ObjectId</classname>, or
<classname>BigInteger</classname>.</para>
<para>Here is a basic example of using the save operation and retrieving
its contents.</para>
<example>
<title>Inserting and retrieving documents using the
MongoTemplate</title>
<programlisting language="java">import static org.springframework.data.mongodb.core.query.Criteria.where;
import static org.springframework.data.mongodb.core.query.Criteria.query;
…
Person p = new Person("Bob", 33);
mongoTemplate.insert(p);
Person qp = mongoTemplate.findOne(query(where("age").is(33)), Person.class); </programlisting>
</example>
<para>The insert/save operations available to you are listed
below.</para>
<para><itemizedlist>
<listitem>
<para><literal>void</literal> <emphasis role="bold">save
</emphasis> <literal>(Object objectToSave) </literal> Save the
object to the default collection.</para>
</listitem>
<listitem>
<para><literal>void</literal> <emphasis role="bold">save
</emphasis> <literal>(Object objectToSave, String collectionName)
</literal> Save the object to the specified collection.</para>
</listitem>
</itemizedlist></para>
<para>A similar set of insert operations is listed below</para>
<para><itemizedlist>
<listitem>
<para><literal>void</literal> <emphasis
role="bold">insert</emphasis> <literal>(Object objectToSave)
</literal> Insert the object to the default collection.</para>
</listitem>
<listitem>
<para><literal>void</literal> <emphasis role="bold">insert
</emphasis> <literal>(Object objectToSave, String collectionName)
</literal> Insert the object to the specified collection.</para>
</listitem>
</itemizedlist></para>
<section id="mongo-template.save-insert.collection">
<title>Which collection will my documents be saved into?</title>
<para>There are two ways to manage the collection name that is used
for operating on the documents. The default collection name that is
used is the class name changed to start with a lower-case letter. So a
<classname>com.test.Person</classname> class would be stored in the
"person" collection. You can customize this by providing a different
collection name using the @Document annotation. You can also override
the collection name by providing your own collection name as the last
parameter for the selected MongoTemplate method calls.</para>
</section>
<section id="mongo-template.save-insert.individual">
<title>Inserting or saving individual objects</title>
<para>The MongoDB driver supports inserting a collection of documents
in one operation. The methods in the MongoOperations interface that
support this functionality are listed below</para>
<para><itemizedlist>
<listitem>
<para><emphasis role="bold">insert</emphasis><literal>
</literal> Insert an object. If there is an existing document
with the same id then an error is generated.</para>
</listitem>
<listitem>
<para><emphasis role="bold">insertAll</emphasis> Takes a
<literal>Collection </literal>of objects as the first parameter.
This method inspects each object and inserts it to the
appropriate collection based on the rules specified
above.</para>
</listitem>
<listitem>
<para><emphasis role="bold">save</emphasis> Save the object
overwriting any object that might exist with the same id.</para>
</listitem>
</itemizedlist></para>
</section>
<section id="mongo-template.save-insert.batch">
<title>Inserting several objects in a batch</title>
<para>The MongoDB driver supports inserting a collection of documents
in one operation. The methods in the MongoOperations interface that
support this functionality are listed below</para>
<para><itemizedlist>
<listitem>
<para><emphasis role="bold">insert</emphasis><literal> methods
that take a Collection</literal><literal> as the first
argument.</literal>This inserts a list of objects in a single
batch write to the database.</para>
</listitem>
</itemizedlist></para>
</section>
</section>
<section id="mongodb-template-update">
<title>Updating documents in a collection</title>
<para>For updates we can elect to update the first document found using
<interfacename>MongoOperation</interfacename>'s method
<literal>updateFirst</literal> or we can update all documents that were
found to match the query using the method
<literal>updateMulti</literal>. Here is an example of an update of all
SAVINGS accounts where we are adding a one time $50.00 bonus to the
balance using the <literal>$inc</literal> operator.</para>
<example>
<title>Updating documents using the MongoTemplate</title>
<programlisting language="java">import static org.springframework.data.mongodb.core.query.Criteria.where;
import static org.springframework.data.mongodb.core.query.Query;
import static org.springframework.data.mongodb.core.query.Update;
...
WriteResult wr = mongoTemplate.updateMulti(new Query(where("accounts.accountType").is(Account.Type.SAVINGS)),
new Update().inc("accounts.$.balance", 50.00),
Account.class);
</programlisting>
</example>
<para>In addition to the <classname>Query</classname> discussed above we
provide the update definition using an <classname>Update</classname>
object. The <classname>Update</classname> class has methods that match
the update modifiers available for MongoDB.</para>
<para>As you can see most methods return the
<classname>Update</classname> object to provide a fluent style for the
API.</para>
<section id="mongodb-template-update.methods">
<title>Methods for executing updates for documents</title>
<para><itemizedlist>
<listitem>
<para><emphasis role="bold">updateFirst </emphasis> Updates the
first document that matches the query document criteria with the
provided updated document.</para>
</listitem>
<listitem>
<para><emphasis role="bold">updateMulti </emphasis> Updates all
objects that match the query document criteria with the provided
updated document.</para>
</listitem>
</itemizedlist></para>
</section>
<section id="mongodb-template-update.update">
<title>Methods for the Update class</title>
<para>The Update class can be used with a little 'syntax sugar' as its
methods are meant to be chained together and you can kick-start the
creation of a new Update instance via the static method
<literal>public static Update update(String key, Object
value)</literal> and using static imports.</para>
<para>Here is a listing of methods on the Update class</para>
<para><itemizedlist>
<listitem>
<para><literal>Update</literal> <emphasis role="bold">addToSet
</emphasis> <literal>(String key, Object value) </literal>
Update using the <literal>$addToSet</literal> update
modifier</para>
</listitem>
<listitem>
<para><literal>Update</literal> <emphasis role="bold">inc
</emphasis> <literal>(String key, Number inc) </literal> Update
using the <literal>$inc</literal> update modifier</para>
</listitem>
<listitem>
<para><literal>Update</literal> <emphasis role="bold">pop
</emphasis> <literal>(String key, Update.Position pos)
</literal> Update using the <literal>$pop</literal> update
modifier</para>
</listitem>
<listitem>
<para><literal>Update</literal> <emphasis role="bold">pull
</emphasis> <literal>(String key, Object value) </literal>
Update using the <literal>$pull</literal> update modifier</para>
</listitem>
<listitem>
<para><literal>Update</literal> <emphasis role="bold">pullAll
</emphasis> <literal>(String key, Object[] values) </literal>
Update using the <literal>$pullAll</literal> update
modifier</para>
</listitem>
<listitem>
<para><literal>Update</literal> <emphasis role="bold">push
</emphasis> <literal>(String key, Object value) </literal>
Update using the <literal>$push</literal> update modifier</para>
</listitem>
<listitem>
<para><literal>Update</literal> <emphasis role="bold">pushAll
</emphasis> <literal>(String key, Object[] values) </literal>
Update using the <literal>$pushAll</literal> update
modifier</para>
</listitem>
<listitem>
<para><literal>Update</literal> <emphasis role="bold">rename
</emphasis> <literal>(String oldName, String newName) </literal>
Update using the <literal>$rename</literal> update
modifier</para>
</listitem>
<listitem>
<para><literal>Update</literal> <emphasis role="bold">set
</emphasis> <literal>(String key, Object value) </literal>
Update using the <literal>$set</literal> update modifier</para>
</listitem>
<listitem>
<para><literal>Update</literal> <emphasis role="bold">unset
</emphasis> <literal>(String key)</literal> Update using the
<literal>$unset</literal> update modifier</para>
</listitem>
</itemizedlist></para>
</section>
</section>
<section id="mongo-template.upserts">
<title>Upserting documents in a collection</title>
<para>Related to performing an <methodname>updateFirst</methodname>
operations, you can also perform an upsert operation which will perform
an insert if no document is found that matches the query. The document
that is inserted is a combination of the query document and the update
document. Here is an example</para>
<programlisting>template.upsert(query(where("ssn").is(1111).and("firstName").is("Joe").and("Fraizer").is("Update")), update("address", addr), Person.class);</programlisting>
</section>
<section id="mongo-template.find-and-upsert">
<title>Finding and Upserting documents in a collection</title>
<para>The <methodname>findAndModify(…)</methodname> method on
DBCollection can update a document and return either the old or newly
updated document in a single operation.
<classname>MongoTemplate</classname> provides a findAndModify method
that takes <classname>Query</classname> and
<classname>Update</classname> classes and converts from
<classname>DBObject</classname> to your POJOs. Here are the
methods</para>
<programlisting language="java">&lt;T&gt; T findAndModify(Query query, Update update, Class&lt;T&gt; entityClass);
&lt;T&gt; T findAndModify(Query query, Update update, Class&lt;T&gt; entityClass, String collectionName);
&lt;T&gt; T findAndModify(Query query, Update update, FindAndModifyOptions options, Class&lt;T&gt; entityClass);
&lt;T&gt; T findAndModify(Query query, Update update, FindAndModifyOptions options, Class&lt;T&gt; entityClass, String collectionName);</programlisting>
<para>As an example usage, we will insert of few
<classname>Person</classname> objects into the container and perform a
simple findAndUpdate operation</para>
<programlisting language="java">mongoTemplate.insert(new Person("Tom", 21));
mongoTemplate.insert(new Person("Dick", 22));
mongoTemplate.insert(new Person("Harry", 23));
Query query = new Query(Criteria.where("firstName").is("Harry"));
Update update = new Update().inc("age", 1);
Person p = mongoTemplate.findAndModify(query, update, Person.class); // return's old person object
assertThat(p.getFirstName(), is("Harry"));
assertThat(p.getAge(), is(23));
p = mongoTemplate.findOne(query, Person.class);
assertThat(p.getAge(), is(24));
// Now return the newly updated document when updating
p = template.findAndModify(query, update, new FindAndModifyOptions().returnNew(true), Person.class);
assertThat(p.getAge(), is(25));</programlisting>
<para>The <classname>FindAndModifyOptions</classname> lets you set the
options of returnNew, upsert, and remove. An example extending off the
previous code snippit is shown below</para>
<programlisting language="java">Query query2 = new Query(Criteria.where("firstName").is("Mary"));
p = mongoTemplate.findAndModify(query2, update, new FindAndModifyOptions().returnNew(true).upsert(true), Person.class);
assertThat(p.getFirstName(), is("Mary"));
assertThat(p.getAge(), is(1));</programlisting>
</section>
<section id="mongo-template.delete">
<title>Methods for removing documents</title>
<para>You can use several overloaded methods to remove an object from
the database.</para>
<para><itemizedlist>
<listitem>
<para><emphasis role="bold">remove</emphasis> Remove the given
document based on one of the following: a specific object
instance, a query document criteria combined with a class or a
query document criteria combined with a specific collection
name.</para>
</listitem>
</itemizedlist></para>
</section>
</section>
<section id="mongo.query">
<title>Querying Documents</title>
<para>You can express your queries using the <classname>Query</classname>
and <classname>Criteria</classname> classes which have method names that
mirror the native MongoDB operator names such as <literal>lt</literal>,
<literal>lte</literal>, <literal>is</literal>, and others. The
<classname>Query</classname> and <classname>Criteria</classname> classes
follow a fluent API style so that you can easily chain together multiple
method criteria and queries while having easy to understand code. Static
imports in Java are used to help remove the need to see the 'new' keyword
for creating <classname>Query</classname> and
<classname>Criteria</classname> instances so as to improve readability. If
you like to create <classname>Query</classname> instances from a plain
JSON String use <classname>BasicQuery</classname>.</para>
<example>
<title>Creating a Query instance from a plain JSON String</title>
<programlisting language="java">BasicQuery query = new BasicQuery("{ age : { $lt : 50 }, accounts.balance : { $gt : 1000.00 }}");
List&lt;Person&gt; result = mongoTemplate.find(query, Person.class); </programlisting>
</example>
<para>GeoSpatial queries are also supported and are described more in the
section <link linkend="mongo.geospatial">GeoSpatial Queries</link>.</para>
<para>Map-Reduce operations are also supported and are described more in
the section <link linkend="mongo.mapreduce">Map-Reduce</link>.</para>
<section id="mongodb-template-query">
<title>Querying documents in a collection</title>
<para>We saw how to retrieve a single document using the findOne and
findById methods on MongoTemplate in previous sections which return a
single domain object. We can also query for a collection of documents to
be returned as a list of domain objects. Assuming that we have a number
of Person objects with name and age stored as documents in a collection
and that each person has an embedded account document with a balance. We
can now run a query using the following code.</para>
<example>
<title>Querying for documents using the MongoTemplate</title>
<programlisting language="java">import static org.springframework.data.mongodb.core.query.Criteria.where;
import static org.springframework.data.mongodb.core.query.Query.query;
…
List&lt;Person&gt; result = mongoTemplate.find(query(where("age").lt(50)
.and("accounts.balance").gt(1000.00d)), Person.class); </programlisting>
</example>
<para>All find methods take a <classname>Query</classname> object as a
parameter. This object defines the criteria and options used to perform
the query. The criteria is specified using a
<classname>Criteria</classname> object that has a static factory method
named <classname>where</classname> used to instantiate a new
<classname>Criteria</classname> object. We recommend using a static
import for
<classname>org.springframework.data.mongodb.core.query.Criteria.where</classname>
and <literal>Query.query</literal> to make the query more
readable.</para>
<para>This query should return a list of <classname>Person</classname>
objects that meet the specified criteria. The
<classname>Criteria</classname> class has the following methods that
correspond to the operators provided in MongoDB.</para>
<para>As you can see most methods return the
<classname>Criteria</classname> object to provide a fluent style for the
API.</para>
<section id="mongodb-template-query.criteria">
<title>Methods for the Criteria class</title>
<para>
<itemizedlist>
<listitem>
<para><literal>Criteria</literal> <emphasis role="bold">all
</emphasis> <literal>(Object o)</literal>Creates a criterion
using the <literal>$all</literal> operator</para>
</listitem>
<listitem>
<para><literal>Criteria</literal> <emphasis role="bold">and
</emphasis> <literal>(String key) </literal>Adds a chained
<classname>Criteria</classname> with the specified
<literal>key</literal> to the current
<classname>Criteria</classname> and returns the newly created
one</para>
</listitem>
<listitem>
<para><literal>Criteria</literal> <emphasis
role="bold">andOperator </emphasis> <literal>(Criteria...
criteria)</literal>Creates an and query using the
<literal>$and</literal> operator for all of the provided
criteria (requires MongoDB 2.0 or later)</para>
</listitem>
<listitem>
<para><literal>Criteria</literal> <emphasis
role="bold">elemMatch </emphasis> <literal>(Criteria c)
</literal>Creates a criterion using the
<literal>$elemMatch</literal> operator</para>
</listitem>
<listitem>
<para><literal>Criteria</literal> <emphasis role="bold">exists
</emphasis> <literal>(boolean b) </literal>Creates a criterion
using the <literal>$exists</literal> operator</para>
</listitem>
<listitem>
<para><literal>Criteria</literal> <emphasis role="bold">gt
</emphasis> <literal>(Object o)</literal>Creates a criterion
using the <literal>$gt</literal> operator</para>
</listitem>
<listitem>
<para><literal>Criteria</literal> <emphasis role="bold">gte
</emphasis> <literal>(Object o)</literal>Creates a criterion
using the <literal>$gte</literal> operator</para>
</listitem>
<listitem>
<para><literal>Criteria</literal> <emphasis role="bold">in
</emphasis> <literal>(Object... o) </literal>Creates a criterion
using the <literal>$in</literal> operator for a varargs
argument.</para>
</listitem>
<listitem>
<para><literal>Criteria</literal> <emphasis role="bold">in
</emphasis> <literal>(Collection&lt;?&gt; collection)
</literal>Creates a criterion using the <literal>$in</literal>
operator using a collection</para>
</listitem>
<listitem>
<para><literal>Criteria</literal> <emphasis role="bold">is
</emphasis> <literal>(Object o)</literal>Creates a criterion
using the <literal>$is</literal> operator</para>
</listitem>
<listitem>
<para><literal>Criteria</literal> <emphasis role="bold">lt
</emphasis> <literal>(Object o)</literal>Creates a criterion
using the <literal>$lt</literal> operator</para>
</listitem>
<listitem>
<para><literal>Criteria</literal> <emphasis role="bold">lte
</emphasis> <literal>(Object o)</literal>Creates a criterion
using the <literal>$lte</literal> operator</para>
</listitem>
<listitem>
<para><literal>Criteria</literal> <emphasis role="bold">mod
</emphasis> <literal>(Number value, Number
remainder)</literal>Creates a criterion using the
<literal>$mod</literal> operator</para>
</listitem>
<listitem>
<para><literal>Criteria</literal> <emphasis role="bold">ne
</emphasis> <literal>(Object o)</literal>Creates a criterion
using the <literal>$ne</literal> operator</para>
</listitem>
<listitem>
<para><literal>Criteria</literal> <emphasis role="bold">nin
</emphasis> <literal>(Object... o) </literal>Creates a criterion
using the <literal>$nin</literal> operator</para>
</listitem>
<listitem>
<para><literal>Criteria</literal> <emphasis
role="bold">norOperator </emphasis> <literal>(Criteria...
criteria)</literal>Creates an nor query using the
<literal>$nor</literal> operator for all of the provided
criteria</para>
</listitem>
<listitem>
<para><literal>Criteria</literal> <emphasis role="bold">not
</emphasis> <literal>()</literal>Creates a criterion using the
<literal>$not</literal> meta operator which affects the clause
directly following</para>
</listitem>
<listitem>
<para><literal>Criteria</literal> <emphasis
role="bold">orOperator </emphasis> <literal>(Criteria...
criteria)</literal>Creates an or query using the
<literal>$or</literal> operator for all of the provided
criteria</para>
</listitem>
<listitem>
<para><literal>Criteria</literal> <emphasis role="bold">regex
</emphasis> <literal>(String re) </literal>Creates a criterion
using a <literal>$regex</literal></para>
</listitem>
<listitem>
<para><literal>Criteria</literal> <emphasis role="bold">size
</emphasis> <literal>(int s)</literal>Creates a criterion using
the <literal>$size</literal> operator</para>
</listitem>
<listitem>
<para><literal>Criteria</literal> <emphasis role="bold">type
</emphasis> <literal>(int t)</literal>Creates a criterion using
the <literal>$type</literal> operator</para>
</listitem>
</itemizedlist>
</para>
</section>
<para>There are also methods on the Criteria class for geospatial
queries. Here is a listing but look at the section on <link
linkend="mongo.geospatial">GeoSpatial Queries</link> to see them in
action.</para>
<itemizedlist>
<listitem>
<para><literal>Criteria</literal> <emphasis role="bold">withinCenter
</emphasis> <literal>(Circle circle)</literal> Creates a geospatial
criterion using <literal>$within $center</literal> operators</para>
</listitem>
<listitem>
<para><literal>Criteria</literal> <emphasis
role="bold">withinCenterSphere </emphasis> <literal>(Circle circle)
</literal>Creates a geospatial criterion using <literal>$within
$center</literal> operators. This is only available for MongoDB 1.7
and higher.</para>
</listitem>
<listitem>
<para><literal>Criteria</literal> <emphasis role="bold">withinBox
</emphasis> <literal>(Box box)</literal> Creates a geospatial
criterion using a <literal>$within $box</literal> operation
<literal/></para>
</listitem>
<listitem>
<para><literal>Criteria</literal> <emphasis role="bold">near
</emphasis> <literal>(Point point)</literal> Creates a geospatial
criterion using a <literal>$near </literal>operation</para>
</listitem>
<listitem>
<para><literal>Criteria</literal> <emphasis role="bold">nearSphere
</emphasis> <literal>(Point point) </literal>Creates a geospatial
criterion using <literal>$nearSphere$center</literal> operations.
This is only available for MongoDB 1.7 and higher.</para>
</listitem>
<listitem>
<para><literal>Criteria</literal> <emphasis role="bold">maxDistance
</emphasis> <literal>(double maxDistance) </literal>Creates a
geospatial criterion using the <literal>$maxDistance</literal>
operation, for use with $near.</para>
</listitem>
</itemizedlist>
<para>The <classname>Query</classname> class has some additional methods
used to provide options for the query.</para>
<section id="mongodb-template-query.query">
<title>Methods for the Query class</title>
<para>
<itemizedlist>
<listitem>
<para><literal>Query</literal> <emphasis role="bold">addCriteria
</emphasis> <literal>(Criteria criteria)</literal> used to add
additional criteria to the query</para>
</listitem>
<listitem>
<para><literal>Field</literal> <emphasis role="bold">fields
</emphasis> <literal>()</literal> used to define fields to be
included in the query results</para>
</listitem>
<listitem>
<para><literal>Query</literal> <emphasis role="bold">limit
</emphasis> <literal>(int limit)</literal> used to limit the
size of the returned results to the provided limit (used for
paging)</para>
</listitem>
<listitem>
<para><literal>Query</literal> <emphasis role="bold">skip
</emphasis> <literal>(int skip)</literal> used to skip the
provided number of documents in the results (used for
paging)</para>
</listitem>
<listitem>
<para><literal>Sort</literal> <emphasis role="bold">sort
</emphasis> <literal>()</literal> used to provide sort
definition for the results</para>
</listitem>
</itemizedlist>
</para>
</section>
</section>
<section id="mongo-template.querying">
<title>Methods for querying for documents</title>
<para>The query methods need to specify the target type T that will be
returned and they are also overloaded with an explicit collection name
for queries that should operate on a collection other than the one
indicated by the return type.</para>
<para><itemizedlist>
<listitem>
<para><emphasis role="bold">findAll </emphasis> Query for a list
of objects of type T from the collection.</para>
</listitem>
<listitem>
<para><emphasis role="bold">findOne</emphasis> Map the results of
an ad-hoc query on the collection to a single instance of an
object of the specified type.</para>
</listitem>
<listitem>
<para><emphasis role="bold">findById</emphasis> Return an object
of the given id and target class.</para>
</listitem>
<listitem>
<para><emphasis role="bold">find</emphasis> Map the results of an
ad-hoc query on the collection to a List of the specified
type.</para>
</listitem>
<listitem>
<para><emphasis role="bold">findAndRemove</emphasis> Map the
results of an ad-hoc query on the collection to a single instance
of an object of the specified type. The first document that
matches the query is returned and also removed from the collection
in the database.</para>
</listitem>
</itemizedlist></para>
</section>
<section id="mongo.geospatial" lang="">
<title>GeoSpatial Queries</title>
<para>MongoDB supports GeoSpatial queries through the use of operators
such as <literal>$near</literal>, <literal>$within</literal>, and
<literal>$nearSphere</literal>. Methods specific to geospatial queries
are available on the <classname>Criteria</classname> class. There are
also a few shape classes, <classname>Box</classname>,
<classname>Circle</classname>, and <classname>Point</classname> that are
used in conjunction with geospatial related
<classname>Criteria</classname> methods.</para>
<para>To understand how to perform GeoSpatial queries we will use the
following Venue class taken from the integration tests.which relies on
using the rich <classname>MappingMongoConverter</classname>.</para>
<programlisting language="java">@Document(collection="newyork")
public class Venue {
@Id
private String id;
private String name;
private double[] location;
@PersistenceConstructor
Venue(String name, double[] location) {
super();
this.name = name;
this.location = location;
}
public Venue(String name, double x, double y) {
super();
this.name = name;
this.location = new double[] { x, y };
}
public String getName() {
return name;
}
public double[] getLocation() {
return location;
}
@Override
public String toString() {
return "Venue [id=" + id + ", name=" + name + ", location="
+ Arrays.toString(location) + "]";
}
}</programlisting>
<para>To find locations within a <classname>Circle</classname>, the
following query can be used.</para>
<programlisting lang="" language="java">Circle circle = new Circle(-73.99171, 40.738868, 0.01);
List&lt;Venue&gt; venues =
template.find(new Query(Criteria.where("location").withinCenter(circle)), Venue.class);</programlisting>
<para>To find venues within a <classname>Circle</classname> using
spherical coordinates the following query can be used</para>
<programlisting lang="" language="java">Circle circle = new Circle(-73.99171, 40.738868, 0.003712240453784);
List&lt;Venue&gt; venues =
template.find(new Query(Criteria.where("location").withinCenterSphere(circle)), Venue.class);</programlisting>
<para>To find venues within a <classname>Box</classname> the following
query can be used</para>
<programlisting language="java">//lower-left then upper-right
Box box = new Box(new Point(-73.99756, 40.73083), new Point(-73.988135, 40.741404));
List&lt;Venue&gt; venues =
template.find(new Query(Criteria.where("location").withinBox(box)), Venue.class);</programlisting>
<para>To find venues near a <classname>Point</classname>, the following
query can be used</para>
<programlisting language="java">Point point = new Point(-73.99171, 40.738868);
List&lt;Venue&gt; venues =
template.find(new Query(Criteria.where("location").near(point).maxDistance(0.01)), Venue.class);</programlisting>
<para>To find venues near a <classname>Point</classname> using spherical
coordines the following query can be used</para>
<programlisting language="java">Point point = new Point(-73.99171, 40.738868);
List&lt;Venue&gt; venues =
template.find(new Query(
Criteria.where("location").nearSphere(point).maxDistance(0.003712240453784)),
Venue.class);
</programlisting>
<section id="mongo.geo-near">
<title>Geo near queries</title>
<para>MongoDB supports querying the database for geo locations and
calculation the distance from a given origin at the very same time.
With geo-near queries it's possible to express queries like: "find all
restaurants in the surrounding 10 miles". To do so
<interfacename>MongoOperations</interfacename> provides
<methodname>geoNear(…)</methodname> methods taking a
<classname>NearQuery</classname> as argument as well as the already
familiar entity type and collection</para>
<programlisting language="java">Point location = new Point(-73.99171, 40.738868);
NearQuery query = NearQuery.near(location).maxDistance(new Distance(10, Metrics.MILES));
GeoResults&lt;Restaurant&gt; = operations.geoNear(query, Restaurant.class);</programlisting>
<para>As you can see we use the <classname>NearQuery</classname>
builder API to set up a query to return all
<classname>Restaurant</classname> instances surrounding the given
<classname>Point</classname> by 10 miles maximum. The
<classname>Metrics</classname> enum used here actually implements an
interface so that other metrics could be plugged into a distance as
well. A <interfacename>Metric</interfacename> is backed by a
multiplier to transform the distance value of the given metric into
native distances. The sample shown here would consider the 10 to be
miles. Using one of the pre-built in metrics (miles and kilometers)
will automatically trigger the spherical flag to be set on the query.
If you want to avoid that, simply hand in plain
<classname>double</classname> values into
<methodname>maxDistance(…)</methodname>. For more information see the
JavaDoc of <classname>NearQuery</classname> and
<classname>Distance</classname>.</para>
<para>The geo near operations return a
<classname>GeoResults</classname> wrapper object that encapsulates
<classname>GeoResult</classname> instances. The wrapping
<classname>GeoResults</classname> allows to access the average
distance of all results. A single <classname>GeoResult</classname>
object simply carries the entity found plus its distance from the
origin.</para>
</section>
</section>
</section>
<section id="mongo.mapreduce">
<title>Map-Reduce Operations</title>
<para>You can query MongoDB using Map-Reduce which is useful for batch
processing, data aggregation, and for when the query language doesn't
fulfill your needs.</para>
<para>Spring provides integration with MongoDB's map reduce by providing
methods on MongoOperations to simplify the creation and execution of
Map-Reduce operations. It can convert the results of a Map-Reduce
operation to a POJO also integrates with Spring's <ulink
url="http://docs.spring.io/spring/docs/current/spring-framework-reference/html/resources.html">Resource
abstraction</ulink> abstraction. This will let you place your JavaScript
files on the file system, classpath, http server or any other Spring
Resource implementation and then reference the JavaScript resources via an
easy URI style syntax, e.g. 'classpath:reduce.js;. Externalizing
JavaScript code in files is often preferable to embedding them as Java
strings in your code. Note that you can still pass JavaScript code as Java
strings if you prefer.</para>
<section id="mongo.mapreduce.example" lang="">
<title>Example Usage</title>
<para>To understand how to perform Map-Reduce operations an example from
the book 'MongoDB - The definitive guide' is used. In this example we
will create three documents that have the values [a,b], [b,c], and [c,d]
respectfully. The values in each document are associated with the key
'x' as shown below. For this example assume these documents are in the
collection named "jmr1". <programlisting>{ "_id" : ObjectId("4e5ff893c0277826074ec533"), "x" : [ "a", "b" ] }
{ "_id" : ObjectId("4e5ff893c0277826074ec534"), "x" : [ "b", "c" ] }
{ "_id" : ObjectId("4e5ff893c0277826074ec535"), "x" : [ "c", "d" ] }
</programlisting> A map function that will count the occurance of each letter
in the array for each document is shown below <programlisting
language="java">function () {
for (var i = 0; i &lt; this.x.length; i++) {
emit(this.x[i], 1);
}
}</programlisting> The reduce function that will sum up the occurance of each
letter across all the documents is shown below <programlisting
language="java">function (key, values) {
var sum = 0;
for (var i = 0; i &lt; values.length; i++)
sum += values[i];
return sum;
}</programlisting> Executing this will result in a collection as shown below.
<programlisting>{ "_id" : "a", "value" : 1 }
{ "_id" : "b", "value" : 2 }
{ "_id" : "c", "value" : 2 }
{ "_id" : "d", "value" : 1 }</programlisting> Assuming that the map and reduce
functions are located in map.js and reduce.js and bundled in your jar so
they are available on the classpath, you can execute a map-reduce
operation and obtain the results as shown below <programlisting
language="java">MapReduceResults&lt;ValueObject&gt; results = mongoOperations.mapReduce("jmr1", "classpath:map.js", "classpath:reduce.js", ValueObject.class);
for (ValueObject valueObject : results) {
System.out.println(valueObject);
}</programlisting> The output of the above code is <programlisting>ValueObject [id=a, value=1.0]
ValueObject [id=b, value=2.0]
ValueObject [id=c, value=2.0]
ValueObject [id=d, value=1.0]</programlisting> The MapReduceResults class
implements <classname>Iterable</classname> and provides access to the
raw output, as well as timing and count statistics. The
<classname>ValueObject</classname> class is simply <programlisting
language="java">public class ValueObject {
private String id;
private float value;
public String getId() {
return id;
}
public float getValue() {
return value;
}
public void setValue(float value) {
this.value = value;
}
@Override
public String toString() {
return "ValueObject [id=" + id + ", value=" + value + "]";
}
}</programlisting> By default the output type of INLINE is used so you don't
have to specify an output collection. To specify additional map-reduce
options use an overloaded method that takes an additional
<classname>MapReduceOptions</classname> argument. The class
<classname>MapReduceOptions</classname> has a fluent API so adding
additional options can be done in a very compact syntax. Here an example
that sets the output collection to "jmr1_out". Note that setting only
the output collection assumes a default output type of REPLACE.
<programlisting language="java">MapReduceResults&lt;ValueObject&gt; results = mongoOperations.mapReduce("jmr1", "classpath:map.js", "classpath:reduce.js",
new MapReduceOptions().outputCollection("jmr1_out"), ValueObject.class);</programlisting>
There is also a static import <literal>import static
org.springframework.data.mongodb.core.mapreduce.MapReduceOptions.options;</literal>
that can be used to make the syntax slightly more compact
<programlisting language="java">MapReduceResults&lt;ValueObject&gt; results = mongoOperations.mapReduce("jmr1", "classpath:map.js", "classpath:reduce.js",
options().outputCollection("jmr1_out"), ValueObject.class);</programlisting>
You can also specify a query to reduce the set of data that will be used
to feed into the map-reduce operation. This will remove the document
that contains [a,b] from consideration for map-reduce operations.
<programlisting language="java">Query query = new Query(where("x").ne(new String[] { "a", "b" }));
MapReduceResults&lt;ValueObject&gt; results = mongoOperations.mapReduce(query, "jmr1", "classpath:map.js", "classpath:reduce.js",
options().outputCollection("jmr1_out"), ValueObject.class);</programlisting>
Note that you can specify additional limit and sort values as well on
the query but not skip values.</para>
</section>
</section>
<section id="mongo.group">
<title>Group Operations</title>
<para>As an alternative to using Map-Reduce to perform data aggregation,
you can use the <ulink
url="http://www.mongodb.org/display/DOCS/Aggregation#Aggregation-Group"><literal>group</literal>
operation</ulink> which feels similar to using SQL's group by query style,
so it may feel more approachable vs. using Map-Reduce. Using the group
operations does have some limitations, for example it is not supported in
a shareded environment and it returns the full result set in a single BSON
object, so the result should be small, less than 10,000 keys.</para>
<para>Spring provides integration with MongoDB's group operation by
providing methods on MongoOperations to simplify the creation and
execution of group operations. It can convert the results of the group
operation to a POJO and also integrates with Spring's <ulink
url="http://docs.spring.io/spring/docs/current/spring-framework-reference/html/resources.html">Resource
abstraction</ulink> abstraction. This will let you place your JavaScript
files on the file system, classpath, http server or any other Spring
Resource implementation and then reference the JavaScript resources via an
easy URI style syntax, e.g. 'classpath:reduce.js;. Externalizing
JavaScript code in files if often preferable to embedding them as Java
strings in your code. Note that you can still pass JavaScript code as Java
strings if you prefer.</para>
<section id="mongo.group.example">
<title>Example Usage</title>
<para>In order to understand how group operations work the following
example is used, which is somewhat artificial. For a more realistic
example consult the book 'MongoDB - The definitive guide'. A collection
named "group_test_collection" created with the following rows.</para>
<programlisting>{ "_id" : ObjectId("4ec1d25d41421e2015da64f1"), "x" : 1 }
{ "_id" : ObjectId("4ec1d25d41421e2015da64f2"), "x" : 1 }
{ "_id" : ObjectId("4ec1d25d41421e2015da64f3"), "x" : 2 }
{ "_id" : ObjectId("4ec1d25d41421e2015da64f4"), "x" : 3 }
{ "_id" : ObjectId("4ec1d25d41421e2015da64f5"), "x" : 3 }
{ "_id" : ObjectId("4ec1d25d41421e2015da64f6"), "x" : 3 }</programlisting>
<para>We would like to group by the only field in each row, the 'x'
field and aggregate the number of times each specific value of 'x'
occurs. To do this we need to create an initial document that contains
our count variable and also a reduce function which will increment it
each time it is encountered. The Java code to execute the group
operation is shown below</para>
<programlisting language="java">GroupByResults&lt;XObject&gt; results = mongoTemplate.group("group_test_collection",
GroupBy.key("x").initialDocument("{ count: 0 }").reduceFunction("function(doc, prev) { prev.count += 1 }"),
XObject.class);</programlisting>
<para>The first argument is the name of the collection to run the group
operation over, the second is a fluent API that specifies properties of
the group operation via a <classname>GroupBy</classname> class. In this
example we are using just the <methodname>intialDocument</methodname>
and <methodname>reduceFunction</methodname> methods. You can also
specify a key-function, as well as a finalizer as part of the fluent
API. If you have multiple keys to group by, you can pass in a comma
separated list of keys.</para>
<para>The raw results of the group operation is a JSON document that
looks like this</para>
<programlisting>{
"retval" : [ { "x" : 1.0 , "count" : 2.0} ,
{ "x" : 2.0 , "count" : 1.0} ,
{ "x" : 3.0 , "count" : 3.0} ] ,
"count" : 6.0 ,
"keys" : 3 ,
"ok" : 1.0
}</programlisting>
<para>The document under the "retval" field is mapped onto the third
argument in the group method, in this case XObject which is shown
below.</para>
<programlisting language="java">public class XObject {
private float x;
private float count;
public float getX() {
return x;
}
public void setX(float x) {
this.x = x;
}
public float getCount() {
return count;
}
public void setCount(float count) {
this.count = count;
}
@Override
public String toString() {
return "XObject [x=" + x + " count = " + count + "]";
}
}</programlisting>
<para>You can also obtain the raw result as a
<classname>DbObject</classname> by calling the method
<methodname>getRawResults</methodname> on the
<classname>GroupByResults</classname> class.</para>
<para>There is an additional method overload of the group method on
<interfacename>MongoOperations</interfacename> which lets you specify a
<classname>Criteria</classname> object for selecting a subset of the
rows. An example which uses a <classname>Criteria</classname> object,
with some syntax sugar using static imports, as well as referencing a
key-function and reduce function javascript files via a Spring Resource
string is shown below.</para>
<programlisting>import static org.springframework.data.mongodb.core.mapreduce.GroupBy.keyFunction;
import static org.springframework.data.mongodb.core.query.Criteria.where;
GroupByResults&lt;XObject&gt; results = mongoTemplate.group(where("x").gt(0),
"group_test_collection",
keyFunction("classpath:keyFunction.js").initialDocument("{ count: 0 }").reduceFunction("classpath:groupReduce.js"), XObject.class);</programlisting>
</section>
</section>
<section id="mongo.aggregation">
<title>Aggregation Framework Support</title>
<para>Spring Data MongoDB provides support for the Aggregation Framework
introduced to MongoDB in version 2.2.</para>
<para>The MongoDB Documentation describes the <ulink
url="http://docs.mongodb.org/manual/core/aggregation/">Aggregation
Framework</ulink> as follows:<quote>The MongoDB aggregation framework
provides a means to calculate aggregated values without having to use
map-reduce. While map-reduce is powerful, it is often more difficult than
necessary for many simple aggregation tasks, such as totaling or averaging
field values.</quote></para>
<para>For further information see the full <ulink
url="http://docs.mongodb.org/manual/aggregation/">reference
documentation</ulink> of the aggregation framework and other data
aggregation tools for MongoDB.</para>
<section id="mongo.aggregation.basic-concepts">
<title>Basic Concepts</title>
<para>The Aggregation Framework support in Spring Data MongoDB is based
on the following key abstractions <classname>Aggregation</classname>,
<classname>AggregationOperation</classname> and
<classname>AggregationResults</classname>.</para>
<itemizedlist>
<listitem>
<para><classname>Aggregation</classname></para>
<para>An Aggregation represents a MongoDB
<methodname>aggregate</methodname> operation and holds the
description of the aggregation pipline instructions. Aggregations
are created by inoking the appropriate
<code>newAggregation(…)</code> static factory Method of the
<classname>Aggregation</classname> class which takes the list of
<classname>AggregateOperation</classname> as a parameter next to the
optional input class.</para>
<para>The actual aggregate operation is executed by the
<methodname>aggregate</methodname> method of the
<classname>MongoTemplate</classname> which also takes the desired
output class as parameter.</para>
</listitem>
<listitem>
<para><classname>AggregationOperation</classname></para>
<para>An <classname>AggregationOperation</classname> represents a
MongoDB aggregation pipeline operation and describes the processing
that should be performed in this aggregation step. Although one
could manually create an <classname>AggregationOperation</classname>
the recommended way to construct an
<classname>AggregateOperation</classname> is to use the static
factory methods provided by the <classname>Aggregate</classname>
class.</para>
</listitem>
<listitem>
<para><classname>AggregationResults</classname></para>
<para><classname>AggregationResults</classname> is the container for
the result of an aggregate operation. It provides access to the raw
aggregation result in the form of an
<classname>DBObject</classname>, to the mapped objects and
information which performed the aggregation.</para>
</listitem>
</itemizedlist>
<para>The canonical example for using the Spring Data MongoDB support
for the MongoDB Aggregation Framework looks as follows:</para>
<programlisting language="java">import static org.springframework.data.mongodb.core.aggregation.Aggregation.*;
Aggregation agg = newAggregation(
pipelineOP1(),
pipelineOP2(),
pipelineOPn()
);
AggregationResults&lt;OutputType&gt; results = mongoTemplate.aggregate(agg, "INPUT_COLLECTION_NAME", OutputType.class);
List&lt;OutputType&gt; mappedResult = results.getMappedResults();
</programlisting>
<para>Note that if you provide an input class as the first parameter to
the <methodname>newAggregation</methodname> method the
<classname>MongoTemplate</classname> will derive the name of the input
collection from this class. Otherwise if you don't not specify an input
class you must provide the name of the input collection explicitly. If
an input-class and an input-collection is provided the latter takes
precedence.</para>
</section>
<section id="mongo.aggregation.supported-aggregation-operations">
<title>Supported Aggregation Operations</title>
<para>The MongoDB Aggregation Framework provides the following types of
Aggregation Operations:</para>
<itemizedlist>
<listitem>
<para>Pipeline Aggregation Operators</para>
</listitem>
<listitem>
<para>Group Aggregation Operators</para>
</listitem>
<listitem>
<para>Boolean Aggregation Operators</para>
</listitem>
<listitem>
<para>Comparison Aggregation Operators</para>
</listitem>
<listitem>
<para>Arithmetic Aggregation Operators</para>
</listitem>
<listitem>
<para>String Aggregation Operators</para>
</listitem>
<listitem>
<para>Date Aggregation Operators</para>
</listitem>
<listitem>
<para>Conditional Aggregation Operators</para>
</listitem>
</itemizedlist>
<para>At the time of this writing we provide support for the following
Aggregation Operations in Spring Data MongoDB.</para>
<table>
<title>Aggregation Operations currently supported by Spring Data
MongoDB</title>
<tgroup cols="2">
<tbody>
<row>
<entry>Pipeline Aggregation Operators</entry>
<entry>project, skip, limit, unwind, group, sort,
geoNear</entry>
</row>
<row>
<entry>Group Aggregation Operators</entry>
<entry>addToSet, first, last, max, min, avg, push, sum,
(*count)</entry>
</row>
<row>
<entry>Arithmetic Aggregation Operators</entry>
<entry>add (*via plus), subtract (*via minus), multiply, divide,
mod</entry>
</row>
<row>
<entry>Comparison Aggregation Operators</entry>
<entry>eq (*via: is), gt, gte, lt, lte, ne</entry>
</row>
</tbody>
</tgroup>
</table>
<para>Note that the aggregation operations not listed here are currently
not supported by Spring Data MongoDB. Comparison aggregation operators
are expressed as <classname>Criteria</classname> expressions.</para>
<para>*) The operation is mapped or added by Spring Data MongoDB.</para>
</section>
<section id="mongo.aggregation.projection">
<title>Projection Expressions</title>
<para>Projection expressions are used to define the fields that are the
outcome of a particular aggregation step. Projection expressions can be
defined via the <methodname>project</methodname> method of the
<classname>Aggregate</classname> class.</para>
<example>
<title>Projection expression examples</title>
<programlisting language="java">project("name", "netPrice") // will generate {$project: {name: 1, netPrice: 1}}
project().and("foo").as("bar") // will generate {$project: {bar: $foo}}
project("a","b").and("foo").as("bar") // will generate {$project: {a: 1, b: 1, bar: $foo}}</programlisting>
<para>Note that more examples for project operations can be found in
the <classname>AggregationTests</classname> class.</para>
</example>
<para>Note that further details regarding the projection expressions can
be found in the <ulink
url="http://docs.mongodb.org/manual/reference/operator/aggregation/project/#pipe._S_project">corresponding
section</ulink> of the MongoDB Aggregation Framework reference
documentation.</para>
<section id="mongo.aggregation.projection.expressions">
<title>Spring Expression Support in Projection Expressions</title>
<para>As of Version 1.4.0 we support the use of SpEL expression in
projection expressions via the <methodname>andExpression</methodname>
method of the <classname>ProjectionOperation</classname> class. This
allows you to define the desired expression as a SpEL expression which
is translated into a corresponding MongoDB projection expression part
on query execution. This makes it much easier to express complex
calculations.</para>
<example>
<title>Complex calculations with SpEL expressions</title>
<para>The following SpEL expression:</para>
<programlisting language="java">1 + (q + 1) / (q - 1)</programlisting>
<para>will be translated into the following projection expression
part:</para>
<programlisting language="javascript">{ "$add" : [ 1, {
"$divide" : [ {
"$add":["$q", 1]}, {
"$subtract":[ "$q", 1]}
]
}]}</programlisting>
</example>
<para>Have a look at an example in more context in <xref
linkend="mongo.aggregation.examples.example5"/> and <xref
linkend="mongo.aggregation.examples.example6"/>. You can find more
usage examples for supported SpEL expression constructs in
<classname>SpelExpressionTransformerUnitTests</classname>.</para>
</section>
</section>
<section id="mongo.aggregation.examples">
<title>Aggregation Framework Examples</title>
<para>The following examples demonstrate the usage patterns for the
MongoDB Aggregation Framework with Spring Data MongoDB.</para>
<example id="mongo.aggregation.examples.example1">
<title>Aggregation Framework Example 1</title>
<para>In this introductory example we want to aggregate a list of tags
to get the occurrence count of a particular tag from a MongoDB
collection called <code>"tags"</code> sorted by the occurrence count
in descending order. This example demonstrates the usage of grouping,
sorting, projections (selection) and unwinding (result
splitting).</para>
<programlisting language="java">class TagCount {
String tag;
int n;
}</programlisting>
<programlisting language="java">import static org.springframework.data.mongodb.core.aggregation.Aggregation.*;
Aggregation agg = newAggregation(
project("tags"),
unwind("tags"),
group("tags").count().as("n"),
project("n").and("tag").previousOperation(),
sort(DESC, "n")
);
AggregationResults&lt;TagCount&gt; results = mongoTemplate.aggregate(agg, "tags", TagCount.class);
List&lt;TagCount&gt; tagCount = results.getMappedResults();</programlisting>
</example>
<itemizedlist>
<listitem>
<para>In order to do this we first create a new aggregation via the
<methodname>newAggregation</methodname> static factory method to
which we pass a list of aggregation operations. These aggregate
operations define the aggregation pipeline of our
<classname>Aggregation</classname>.</para>
</listitem>
<listitem>
<para>As a second step we select the <code>"tags"</code> field
(which is an array of strings) from the input collection with the
<methodname>project</methodname> operation.</para>
</listitem>
<listitem>
<para>In a third step we use the <methodname>unwind</methodname>
operation to generate a new document for each tag within the
<code>"tags"</code> array.</para>
</listitem>
<listitem>
<para>In the forth step we use the <methodname>group</methodname>
operation to define a group for each <code>"tags"</code>-value for
which we aggregate the occurrence count via the
<methodname>count</methodname> aggregation operator and collect the
result in a new field called <code>"n"</code>.</para>
</listitem>
<listitem>
<para>As a fifth step we select the field <code>"n"</code> and
create an alias for the id-field generated from the previous group
operation (hence the call to <code>previousOperation()</code>) with
the name <code>"tag"</code>.</para>
</listitem>
<listitem>
<para>As the sixth step we sort the resulting list of tags by their
occurrence count in descending order via the
<methodname>sort</methodname> operation.</para>
</listitem>
<listitem>
<para>Finally we call the <methodname>aggregate</methodname> Method
on the MongoTemplate in order to let MongoDB perform the acutal
aggregation operation with the created
<classname>Aggregation</classname> as an argument.</para>
</listitem>
</itemizedlist>
<para>Note that the input collection is explicitly specified as the
<code>"tags"</code> parameter to the <methodname>aggregate</methodname>
Method. If the name of the input collection is not specified explicitly,
it is derived from the input-class passed as first parameter to the
<methodname>newAggreation</methodname> Method.</para>
<example id="mongo.aggregation.examples.example2">
<title>Aggregation Framework Example 2</title>
<para>This example is based on the <ulink
url="http://docs.mongodb.org/manual/tutorial/aggregation-examples/#largest-and-smallest-cities-by-state">Largest
and Smallest Cities by State</ulink> example from the MongoDB
Aggregation Framework documentation. We added additional sorting to
produce stable results with different MongoDB versions. Here we want
to return the smallest and largest cities by population for each
state, using the aggregation framework. This example demonstrates the
usage of grouping, sorting and projections (selection).</para>
<programlisting language="java">class ZipInfo {
String id;
String city;
String state;
@Field("pop") int population;
@Field("loc") double[] location;
}
class City {
String name;
int population;
}
class ZipInfoStats {
String id;
String state;
City biggestCity;
City smallestCity;
}</programlisting>
<programlisting language="java">import static org.springframework.data.mongodb.core.aggregation.Aggregation.*;
TypedAggregation&lt;ZipInfo&gt; aggregation = newAggregation(ZipInfo.class,
group("state", "city")
.sum("population").as("pop"),
sort(ASC, "pop", "state", "city"),
group("state")
.last("city").as("biggestCity")
.last("pop").as("biggestPop")
.first("city").as("smallestCity")
.first("pop").as("smallestPop"),
project()
.and("state").previousOperation()
.and("biggestCity")
.nested(bind("name", "biggestCity").and("population", "biggestPop"))
.and("smallestCity")
.nested(bind("name", "smallestCity").and("population", "smallestPop")),
sort(ASC, "state")
);
AggregationResults&lt;ZipInfoStats&gt; result = mongoTemplate.aggregate(aggregation, ZipInfoStats.class);
ZipInfoStats firstZipInfoStats = result.getMappedResults().get(0);
</programlisting>
</example>
<itemizedlist>
<listitem>
<para>The class <classname>ZipInfo</classname> maps the structure of
the given input-collection. The class
<classname>ZipInfoStats</classname> defines the structure in the
desired output format.</para>
</listitem>
<listitem>
<para>As a first step we use the <methodname>group</methodname>
operation to define a group from the input-collection. The grouping
criteria is the combination of the fields <code>"state"</code> and
<code>"city" </code>which forms the id structure of the group. We
aggregate the value of the <code>"population"</code> property from
the grouped elements with by using the <methodname>sum</methodname>
operator saving the result in the field <code>"pop"</code>.</para>
</listitem>
<listitem>
<para>In a second step we use the <methodname>sort</methodname>
operation to sort the intermediate-result by the fields
<code>"pop"</code>, <code>"state"</code> and <code>"city"</code> in
ascending order, such that the smallest city is at the top and the
biggest city is at the bottom of the result. Note that the sorting
on "state" and <code>"city"</code> is implicitly performed against
the group id fields which Spring Data MongoDB took care of.</para>
</listitem>
<listitem>
<para>In the third step we use a <methodname>group</methodname>
operation again to group the intermediate result by
<code>"state"</code>. Note that <code>"state"</code> again
implicitly references an group-id field. We select the name and the
population count of the biggest and smallest city with calls to the
<code>last(…)</code> and <code>first(...)</code> operator
respectively via the <methodname>project</methodname>
operation.</para>
</listitem>
<listitem>
<para>As the forth step we select the <code>"state"</code> field
from the previous <methodname>group</methodname> operation. Note
that <code>"state"</code> again implicitly references an group-id
field. As we do not want an implicit generated id to appear, we
exclude the id from the previous operation via
<code>and(previousOperation()).exclude()</code>. As we want to
populate the nested <classname>City</classname> structures in our
output-class accordingly we have to emit appropriate sub-documents
with the nested method.</para>
</listitem>
<listitem>
<para>Finally as the fifth step we sort the resulting list of
<classname>StateStats</classname> by their state name in ascending
order via the <methodname>sort</methodname> operation.</para>
</listitem>
</itemizedlist>
<para>Note that we derive the name of the input-collection from the
<classname>ZipInfo</classname>-class passed as first parameter to the
<methodname>newAggregation</methodname>-Method.</para>
<example id="mongo.aggregation.examples.example3">
<title>Aggregation Framework Example 3</title>
<para>This example is based on the <ulink
url="http://docs.mongodb.org/manual/tutorial/aggregation-examples/#states-with-populations-over-10-million">States
with Populations Over 10 Million </ulink>example from the MongoDB
Aggregation Framework documentation. We added additional sorting to
produce stable results with different MongoDB versions. Here we want
to return all states with a population greater than 10 million, using
the aggregation framework. This example demonstrates the usage of
grouping, sorting and matching (filtering).</para>
<programlisting language="java">class StateStats {
@Id String id;
String state;
@Field("totalPop") int totalPopulation;
}</programlisting>
<programlisting language="java">import static org.springframework.data.mongodb.core.aggregation.Aggregation.*;
TypedAggregation&lt;ZipInfo&gt; agg = newAggregation(ZipInfo.class,
group("state").sum("population").as("totalPop"),
sort(ASC, previousOperation(), "totalPop"),
match(where("totalPop").gte(10 * 1000 * 1000))
);
AggregationResults&lt;StateStats&gt; result = mongoTemplate.aggregate(agg, StateStats.class);
List&lt;StateStats&gt; stateStatsList = result.getMappedResults();</programlisting>
</example>
<itemizedlist>
<listitem>
<para>As a first step we group the input collection by the
<code>"state"</code> field and calculate the sum of the
<code>"population"</code> field and store the result in the new
field <code>"totalPop"</code>.</para>
</listitem>
<listitem>
<para>In the second step we sort the intermediate result by the
id-reference of the previous group operation in addition to the
<code>"totalPop"</code> field in ascending order.</para>
</listitem>
<listitem>
<para>Finally in the third step we filter the intermediate result by
using a <methodname>match</methodname> operation which accepts a
<classname>Criteria</classname> query as an argument.</para>
</listitem>
</itemizedlist>
<para>Note that we derive the name of the input-collection from the
<classname>ZipInfo</classname>-class passed as first parameter to the
<methodname>newAggregation</methodname>-Method.</para>
<example id="mongo.aggregation.examples.example4">
<title>Aggregation Framework Example 4</title>
<para>This example demonstrates the use of simple arithmetic
operations in the projection operation.</para>
<programlisting language="java">class Product {
String id;
String name;
double netPrice;
int spaceUnits;
}</programlisting>
<programlisting language="java">import static org.springframework.data.mongodb.core.aggregation.Aggregation.*;
TypedAggregation&lt;Product&gt; agg = newAggregation(Product.class,
project("name", "netPrice")
.and("netPrice").plus(1).as("netPricePlus1")
.and("netPrice").minus(1).as("netPriceMinus1")
.and("netPrice").multiply(1.19).as("grossPrice")
.and("netPrice").divide(2).as("netPriceDiv2")
.and("spaceUnits").mod(2).as("spaceUnitsMod2")
);
AggregationResults&lt;DBObject&gt; result = mongoTemplate.aggregate(agg, DBObject.class);
List&lt;DBObject&gt; resultList = result.getMappedResults();</programlisting>
</example>
<para>Note that we derive the name of the input-collection from the
<classname>Product</classname>-class passed as first parameter to the
<methodname>newAggregation</methodname>-Method.</para>
<example id="mongo.aggregation.examples.example5">
<title>Aggregation Framework Example 5</title>
<para>This example demonstrates the use of simple arithmetic
operations derived from SpEL Expressions in the projection
operation.</para>
<programlisting language="java">class Product {
String id;
String name;
double netPrice;
int spaceUnits;
}</programlisting>
<programlisting language="java">import static org.springframework.data.mongodb.core.aggregation.Aggregation.*;
TypedAggregation&lt;Product&gt; agg = newAggregation(Product.class,
project("name", "netPrice")
.andExpression("netPrice + 1").as("netPricePlus1")
.andExpression("netPrice - 1").as("netPriceMinus1")
.andExpression("netPrice / 2").as("netPriceDiv2")
.andExpression("netPrice * 1.19").as("grossPrice")
.andExpression("spaceUnits % 2").as("spaceUnitsMod2")
.andExpression("(netPrice * 0.8 + 1.2) * 1.19").as("grossPriceIncludingDiscountAndCharge")
);
AggregationResults&lt;DBObject&gt; result = mongoTemplate.aggregate(agg, DBObject.class);
List&lt;DBObject&gt; resultList = result.getMappedResults();</programlisting>
</example>
<example id="mongo.aggregation.examples.example6">
<title>Aggregation Framework Example 6</title>
<para>This example demonstrates the use of complex arithmetic
operations derived from SpEL Expressions in the projection
operation.</para>
<para>Note: The additional parameters passed to the
<methodname>addExpression</methodname> Method can be referenced via
indexer expressions according to their position. In this example we
reference the parameter <varname>shippingCosts</varname> which is the
first parameter of the parameters array via <code>[0]</code>. External
parameter expressions are replaced with their respective values when
the SpEL expression is transformed into a MongoDB aggregation
framework expression.</para>
<programlisting language="java">class Product {
String id;
String name;
double netPrice;
int spaceUnits;
}</programlisting>
<programlisting language="java">import static org.springframework.data.mongodb.core.aggregation.Aggregation.*;
double shippingCosts = 1.2;
TypedAggregation&lt;Product&gt; agg = newAggregation(Product.class,
project("name", "netPrice")
.andExpression("(netPrice * (1-discountRate) + [0]) * (1+taxRate)", shippingCosts).as("salesPrice")
);
AggregationResults&lt;DBObject&gt; result = mongoTemplate.aggregate(agg, DBObject.class);
List&lt;DBObject&gt; resultList = result.getMappedResults();</programlisting>
</example>
<para>Note that we can also refer to other fields of the document within
the SpEL expression.</para>
</section>
</section>
<section id="mongo.custom-converters">
<title>Overriding default mapping with custom converters</title>
<para>In order to have more fine grained control over the mapping process
you can register Spring converters with the
<classname>MongoConverter</classname> implementations such as the
<classname>MappingMongoConverter</classname>.</para>
<para>The <classname>MappingMongoConverter</classname> checks to see if
there are any Spring converters that can handle a specific class before
attempting to map the object itself. To 'hijack' the normal mapping
strategies of the <classname>MappingMongoConverter</classname>, perhaps
for increased performance or other custom mapping needs, you first need to
create an implementation of the Spring
<interfacename>Converter</interfacename> interface and then register it
with the MappingConverter.</para>
<note>
<para>For more information on the Spring type conversion service see the
reference docs <ulink
url="http://docs.spring.io/spring/docs/current/spring-framework-reference/html/validation.html#core-convert">here</ulink>.</para>
</note>
<section id="mongo.custom-converters.writer">
<title>Saving using a registered Spring Converter</title>
<para>An example implementation of the
<interfacename>Converter</interfacename> that converts from a Person
object to a <classname>com.mongodb.DBObject</classname> is shown
below</para>
<programlisting language="java">import org.springframework.core.convert.converter.Converter;
import com.mongodb.BasicDBObject;
import com.mongodb.DBObject;
public class PersonWriteConverter implements Converter&lt;Person, DBObject&gt; {
public DBObject convert(Person source) {
DBObject dbo = new BasicDBObject();
dbo.put("_id", source.getId());
dbo.put("name", source.getFirstName());
dbo.put("age", source.getAge());
return dbo;
}
}</programlisting>
</section>
<section id="mongo.custom-converters.reader">
<title>Reading using a Spring Converter</title>
<para>An example implementation of a Converter that converts from a
DBObject ot a Person object is shownn below</para>
<programlisting language="java">public class PersonReadConverter implements Converter&lt;DBObject, Person&gt; {
public Person convert(DBObject source) {
Person p = new Person((ObjectId) source.get("_id"), (String) source.get("name"));
p.setAge((Integer) source.get("age"));
return p;
}
}</programlisting>
</section>
<section id="mongo.custom-converters.xml">
<title>Registering Spring Converters with the MongoConverter</title>
<para>The Mongo Spring namespace provides a convenience way to register
Spring <interfacename>Converter</interfacename>s with the
<classname>MappingMongoConverter</classname>. The configuration snippet
below shows how to manually register converter beans as well as
configuring the wrapping <classname>MappingMongoConverter</classname>
into a <classname>MongoTemplate</classname>.</para>
<programlisting language="xml">&lt;mongo:db-factory dbname="database"/&gt;
&lt;mongo:mapping-converter&gt;
&lt;mongo:custom-converters&gt;
&lt;mongo:converter ref="readConverter"/&gt;
&lt;mongo:converter&gt;
&lt;bean class="org.springframework.data.mongodb.test.PersonWriteConverter"/&gt;
&lt;/mongo:converter&gt;
&lt;/mongo:custom-converters&gt;
&lt;/mongo:mapping-converter&gt;
&lt;bean id="readConverter" class="org.springframework.data.mongodb.test.PersonReadConverter"/&gt;
&lt;bean id="mongoTemplate" class="org.springframework.data.mongodb.core.MongoTemplate"&gt;
&lt;constructor-arg name="mongoDbFactory" ref="mongoDbFactory"/&gt;
&lt;constructor-arg name="mongoConverter" ref="mappingConverter"/&gt;
&lt;/bean&gt;</programlisting>
<para>You can also use the base-package attribute of the
custom-converters element to enable classpath scanning for all
<interfacename>Converter</interfacename> and
<interfacename>GenericConverter</interfacename> implementations below
the given package.</para>
<programlisting language="xml">&lt;mongo:mapping-converter&gt;
&lt;mongo:custom-converters base-package="com.acme.**.converters" /&gt;
&lt;/mongo:mapping-converter&gt;</programlisting>
</section>
<section id="mongo.converter-disambiguation">
<title>Converter disambiguation</title>
<para>Generally we inspect the <interfacename>Converter</interfacename>
implementations for the source and target types they convert from and
to. Depending on whether one of those is a type MongoDB can handle
natively we will register the converter instance as reading or writing
one. Have a look at the following samples:</para>
<programlisting language="java">// Write converter as only the target type is one Mongo can handle natively
class MyConverter implements Converter&lt;Person, String&gt; { … }
// Read converter as only the source type is one Mongo can handle natively
class MyConverter implements Converter&lt;String, Person&gt; { … }</programlisting>
<para>In case you write a <interfacename>Converter</interfacename> whose
source and target type are native Mongo types there's no way for us to
determine whether we should consider it as reading or writing converter.
Registering the converter instance as both might lead to unwanted
results then. E.g. a <interfacename>Converter&lt;String,
Long&gt;</interfacename> is ambiguous although it probably does not make
sense to try to convert all <classname>String</classname>s into
<classname>Long</classname>s when writing. To be generally able to force
the infrastructure to register a converter for one way only we provide
<interfacename>@ReadingConverter</interfacename> as well as
<interfacename>@WritingConverter</interfacename> to be used at the
converter implementation.</para>
</section>
</section>
<section id="mongo-template.index-and-collections">
<title>Index and Collection management</title>
<para><classname>MongoTemplate</classname> provides a few methods for
managing indexes and collections. These are collected into a helper
interface called <interfacename>IndexOperations</interfacename>. You
access these operations by calling the method
<methodname>indexOps</methodname> and pass in either the collection name
or the <literal>java.lang.Class</literal> of your entity (the collection
name will be derived from the .class either by name or via annotation
metadata).</para>
<para>The <interfacename>IndexOperations</interfacename> interface is
shown below</para>
<programlisting language="java">public interface IndexOperations {
void ensureIndex(IndexDefinition indexDefinition);
void dropIndex(String name);
void dropAllIndexes();
void resetIndexCache();
List&lt;IndexInfo&gt; getIndexInfo();
}</programlisting>
<section id="mongo-template.index-and-collections.index">
<title>Methods for creating an Index</title>
<para>We can create an index on a collection to improve query
performance.</para>
<example>
<title>Creating an index using the MongoTemplate</title>
<programlisting language="java">mongoTemplate.indexOps(Person.class).ensureIndex(new Index().on("name",Order.ASCENDING)); </programlisting>
</example>
<para><itemizedlist>
<listitem>
<para><emphasis role="bold">ensureIndex </emphasis>Ensure that an
index for the provided IndexDefinition exists for the
collection.</para>
</listitem>
</itemizedlist></para>
<para>You can create both standard indexes and geospatial indexes using
the classes <classname>IndexDefinition</classname> and
<classname>GeoSpatialIndex</classname> respectfully. For example, given
the Venue class defined in a previous section, you would declare a
geospatial query as shown below</para>
<programlisting language="java">mongoTemplate.indexOps(Venue.class).ensureIndex(new GeospatialIndex("location"));</programlisting>
</section>
<section id="mongo-template.index-and-collections.access">
<title>Accessing index information</title>
<para>The IndexOperations interface has the method getIndexInfo that
returns a list of IndexInfo objects. This contains all the indexes
defined on the collectcion. Here is an example that defines an index on
the Person class that has age property.</para>
<programlisting language="java">template.indexOps(Person.class).ensureIndex(new Index().on("age", Order.DESCENDING).unique(Duplicates.DROP));
List&lt;IndexInfo&gt; indexInfoList = template.indexOps(Person.class).getIndexInfo();
// Contains
// [IndexInfo [fieldSpec={_id=ASCENDING}, name=_id_, unique=false, dropDuplicates=false, sparse=false],
// IndexInfo [fieldSpec={age=DESCENDING}, name=age_-1, unique=true, dropDuplicates=true, sparse=false]]
</programlisting>
</section>
<section id="mongo-template.index-and-collections.collection">
<title>Methods for working with a Collection</title>
<para>It's time to look at some code examples showing how to use the
<classname>MongoTemplate</classname>. First we look at creating our
first collection.</para>
<example>
<title>Working with collections using the MongoTemplate</title>
<programlisting language="java">DBCollection collection = null;
if (!mongoTemplate.getCollectionNames().contains("MyNewCollection")) {
collection = mongoTemplate.createCollection("MyNewCollection");
}
mongoTemplate.dropCollection("MyNewCollection"); </programlisting>
</example>
<para><itemizedlist>
<listitem>
<para><emphasis role="bold">getCollectionNames</emphasis> Returns
a set of collection names.</para>
</listitem>
<listitem>
<para><emphasis role="bold">collectionExists</emphasis> Check to
see if a collection with a given name exists.</para>
</listitem>
<listitem>
<para><emphasis role="bold">createCollection</emphasis> Create an
uncapped collection</para>
</listitem>
<listitem>
<para><emphasis role="bold">dropCollection</emphasis> Drop the
collection</para>
</listitem>
<listitem>
<para><emphasis role="bold">getCollection</emphasis> Get a
collection by name, creating it if it doesn't exist.</para>
</listitem>
</itemizedlist></para>
</section>
</section>
<section id="mongo-template.commands">
<title>Executing Commands</title>
<para>You can also get at the MongoDB driver's <classname>DB.command(
)</classname> method using the <methodname>executeCommand(…)</methodname>
methods on <classname>MongoTemplate</classname>. These will also perform
exception translation into Spring's
<classname>DataAccessException</classname> hierarchy.</para>
<section id="mongo-template.commands.execution">
<title>Methods for executing commands</title>
<para><itemizedlist>
<listitem>
<para><literal>CommandResult</literal> <emphasis
role="bold">executeCommand </emphasis> <literal>(DBObject command)
</literal> Execute a MongoDB command.</para>
</listitem>
<listitem>
<para><literal>CommandResult</literal> <emphasis
role="bold">executeCommand </emphasis> <literal>(String
jsonCommand) </literal> Execute the a MongoDB command expressed as
a JSON string.</para>
</listitem>
</itemizedlist></para>
</section>
</section>
<section id="mongodb.mapping-usage.events">
<title>Lifecycle Events</title>
<para>Built into the MongoDB mapping framework are several
<classname>org.springframework.context.ApplicationEvent</classname> events
that your application can respond to by registering special beans in the
<code>ApplicationContext</code>. By being based off Spring's
ApplicationContext event infastructure this enables other products, such
as Spring Integration, to easily receive these events as they are a well
known eventing mechanism in Spring based applications.</para>
<para>To intercept an object before it goes through the conversion process
(which turns your domain object into a
<classname>com.mongodb.DBObject</classname>), you'd register a subclass of
<classname>AbstractMongoEventListener</classname> that overrides the
<code>onBeforeConvert</code> method. When the event is dispatched, your
listener will be called and passed the domain object before it goes into
the converter.</para>
<example>
<programlisting language="java">public class BeforeConvertListener extends AbstractMongoEventListener&lt;Person&gt; {
@Override
public void onBeforeConvert(Person p) {
... does some auditing manipulation, set timestamps, whatever ...
}
} </programlisting>
</example>
<para>To intercept an object before it goes into the database, you'd
register a subclass of
<classname>org.springframework.data.mongodb.core.mapping.event.AbstractMongoEventListener</classname>
that overrides the <code>onBeforeSave</code> method. When the event is
dispatched, your listener will be called and passed the domain object and
the converted <classname>com.mongodb.DBObject</classname>.</para>
<example>
<programlisting language="java">public class BeforeSaveListener extends AbstractMongoEventListener&lt;Person&gt; {
@Override
public void onBeforeSave(Person p, DBObject dbo) {
… change values, delete them, whatever …
}
} </programlisting>
</example>
<para>Simply declaring these beans in your Spring ApplicationContext will
cause them to be invoked whenever the event is dispatched.</para>
<para>The list of callback methods that are present in
AbstractMappingEventListener are</para>
<itemizedlist>
<listitem>
<para><methodname>onBeforeConvert</methodname> - called in
MongoTemplate insert, insertList and save operations before the object
is converted to a DBObject using a MongoConveter.</para>
</listitem>
<listitem>
<para><methodname>onBeforeSave</methodname> - called in MongoTemplate
insert, insertList and save operations <emphasis>before</emphasis>
inserting/saving the DBObject in the database.</para>
</listitem>
<listitem>
<para><methodname>onAfterSave</methodname> - called in MongoTemplate
insert, insertList and save operations <emphasis>after</emphasis>
inserting/saving the DBObject in the database.</para>
</listitem>
<listitem>
<para><methodname>onAfterLoad</methodname> - called in MongoTempnlate
find, findAndRemove, findOne and getCollection methods after the
DBObject is retrieved from the database.</para>
</listitem>
<listitem>
<para><methodname>onAfterConvert</methodname> - called in
MongoTempnlate find, findAndRemove, findOne and getCollection methods
after the DBObject retrieved from the database was converted to a
POJO.</para>
</listitem>
</itemizedlist>
</section>
<section id="mongo.exception">
<title>Exception Translation</title>
<para>The Spring framework provides exception translation for a wide
variety of database and mapping technologies. This has traditionally been
for JDBC and JPA. The Spring support for MongoDB extends this feature to
the MongoDB Database by providing an implementation of the
<classname>org.springframework.dao.support.PersistenceExceptionTranslator</classname>
interface.</para>
<para>The motivation behind mapping to Spring's <ulink
url="http://docs.spring.io/spring/docs/current/spring-framework-reference/html/dao.html#dao-exceptions">consistent
data access exception hierarchy</ulink> is that you are then able to write
portable and descriptive exception handling code without resorting to
coding against <ulink
url="http://www.mongodb.org/about/contributors/error-codes/">MongoDB error
codes</ulink>. All of Spring's data access exceptions are inherited from
the root <classname>DataAccessException</classname> class so you can be
sure that you will be able to catch all database related exception within
a single try-catch block. Note, that not all exceptions thrown by the
MongoDB driver inherit from the MongoException class. The inner exception
and message are preserved so no information is lost.</para>
<para>Some of the mappings performed by the
<classname>MongoExceptionTranslator</classname> are: com.mongodb.Network
to DataAccessResourceFailureException and
<classname>MongoException</classname> error codes 1003, 12001, 12010,
12011, 12012 to <classname>InvalidDataAccessApiUsageException</classname>.
Look into the implementation for more details on the mapping.</para>
</section>
<section id="mongo.executioncallback">
<title>Execution callbacks</title>
<para>One common design feature of all Spring template classes is that all
functionality is routed into one of the templates execute callback
methods. This helps ensure that exceptions and any resource management
that maybe required are performed consistency. While this was of much
greater need in the case of JDBC and JMS than with MongoDB, it still
offers a single spot for exception translation and logging to occur. As
such, using thexe execute callback is the preferred way to access the
MongoDB driver's <classname>DB</classname> and
<classname>DBCollection</classname> objects to perform uncommon operations
that were not exposed as methods on
<classname>MongoTemplate</classname>.</para>
<para>Here is a list of execute callback methods.</para>
<para><itemizedlist>
<listitem>
<para><literal>&lt;T&gt; T</literal> <emphasis role="bold">execute
</emphasis> <literal>(Class&lt;?&gt; entityClass,
CollectionCallback&lt;T&gt; action) </literal> Executes the given
CollectionCallback for the entity collection of the specified
class.</para>
</listitem>
<listitem>
<para><literal>&lt;T&gt; T</literal> <emphasis role="bold">execute
</emphasis> <literal>(String collectionName,
CollectionCallback&lt;T&gt; action) </literal> Executes the given
CollectionCallback on the collection of the given name.</para>
</listitem>
<listitem>
<para><literal>&lt;T&gt; T</literal> <emphasis role="bold">execute
</emphasis> <literal>(DbCallback&lt;T&gt; action) Spring Data
MongoDB provides support for the Aggregation Framework introduced to
MongoDB in version 2.2.</literal> Executes a DbCallback translating
any exceptions as necessary.</para>
</listitem>
<listitem>
<para><literal>&lt;T&gt; T</literal> <emphasis role="bold">execute
</emphasis> <literal>(String collectionName, DbCallback&lt;T&gt;
action) </literal> Executes a DbCallback on the collection of the
given name translating any exceptions as necessary.</para>
</listitem>
<listitem>
<para><literal>&lt;T&gt; T</literal> <emphasis
role="bold">executeInSession </emphasis>
<literal>(DbCallback&lt;T&gt; action) </literal> Executes the given
DbCallback within the same connection to the database so as to
ensure consistency in a write heavy environment where you may read
the data that you wrote.</para>
</listitem>
</itemizedlist></para>
<para>Here is an example that uses the
<interfacename>CollectionCallback</interfacename> to return information
about an index</para>
<programlisting language="java">boolean hasIndex = template.execute("geolocation", new CollectionCallbackBoolean&gt;() {
public Boolean doInCollection(Venue.class, DBCollection collection) throws MongoException, DataAccessException {
List&lt;DBObject&gt; indexes = collection.getIndexInfo();
for (DBObject dbo : indexes) {
if ("location_2d".equals(dbo.get("name"))) {
return true;
}
}
return false;
}
});</programlisting>
</section>
<section id="gridfs">
<title>GridFS support</title>
<para>MongoDB supports storing binary files inside it's filesystem GridFS.
Spring Data MongoDB provides a
<interfacename>GridFsOperations</interfacename> interface as well as the
according implementation <classname>GridFsTemplate</classname> to easily
interact with the filesystem. You can setup a
<classname>GridFsTemplate</classname> instance by handing it a
<interfacename>MongoDbFactory</interfacename> as well as a
<interfacename>MongoConverter</interfacename>:</para>
<example>
<title>JavaConfig setup for a GridFsTemplate</title>
<programlisting language="java">class GridFsConfiguration extends AbstractMongoConfiguration {
// … further configuration omitted
@Bean
public GridFsTemplate gridFsTemplate() {
return new GridFsTemplate(mongoDbFactory(), mappingMongoConverter());
}
}</programlisting>
</example>
<para>An according XML configuration looks like this:</para>
<example>
<title>XML configuration for a GridFsTemplate</title>
<programlisting language="xml">&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:mongo="http://www.springframework.org/schema/data/mongo"
xsi:schemaLocation="http://www.springframework.org/schema/data/mongo
http://www.springframework.org/schema/data/mongo/spring-mongo.xsd
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd"&gt;
&lt;mongo:db-factory id="mongoDbFactory" dbname="database" /&gt;
&lt;mongo:mapping-converter id="converter" /&gt;
&lt;bean class="org.springframework.data.mongodb.gridfs.GridFsTemplate"&gt;
&lt;constructor-arg ref="mongoDbFactory" /&gt;
&lt;constructor-arg ref="converter" /&gt;
&lt;/bean&gt;
&lt;/beans&gt;</programlisting>
</example>
<para>The template can now be injected and used to perform storage and
retrieval operations.</para>
<example>
<title>Using GridFsTemplate to store files</title>
<programlisting language="java">class GridFsClient {
@Autowired
GridFsOperations operations;
@Test
public void storeFileToGridFs {
FileMetadata metadata = new FileMetadata();
// populate metadata
Resource file = … // lookup File or Resource
operations.store(file.getInputStream(), "filename.txt", metadata);
}
}</programlisting>
</example>
<para>The <methodname>store(…)</methodname> operations take an
<interfacename>InputStream</interfacename>, a filename and optionally
metadata information about the file to store. The metadata can be an
arbitrary object which will be marshalled by the
<interfacename>MongoConverter</interfacename> configured with the
<classname>GridFsTemplate</classname>. Alternatively you can also provide
a <interfacename>DBObject</interfacename> as well.</para>
<para>Reading files from the filesystem can either be achieved through the
<methodname>find(…)</methodname> or
<methodname>getResources(…)</methodname> methods. Let's have a look at the
<methodname>find(…)</methodname> methods first. You can either find a
single file matching a <classname>Query</classname> or multiple ones. To
easily define file queries we provide the
<classname>GridFsCriteria</classname> helper class. It provides static
factory methods to encapsulate default metadata fields (e.g.
<methodname>whereFilename()</methodname>,
<methodname>whereContentType()</methodname>) or the custom one through
<methodname>whereMetaData()</methodname>.</para>
<example>
<title>Using GridFsTemplate to query for files</title>
<programlisting language="java">class GridFsClient {
@Autowired
GridFsOperations operations;
@Test
public void findFilesInGridFs {
List&lt;GridFSDBFile&gt; result = operations.find(query(whereFilename().is("filename.txt")))
}
}</programlisting>
</example>
<note>
<para>Currently MongoDB does not support defining sort criterias when
retrieving files from GridFS. Thus any sort criterias defined on the
<classname>Query</classname> instance handed into the
<methodname>find(…)</methodname> method will be disregarded.</para>
</note>
<para>The other option to read files from the GridFs is using the methods
introduced by the <interfacename>ResourcePatternResolver</interfacename>
interface. They allow handing an Ant path into the method ar thus retrieve
files matching the given pattern.</para>
<example>
<title>Using GridFsTemplate to read files</title>
<programlisting language="java">class GridFsClient {
@Autowired
GridFsOperations operations;
@Test
public void readFilesFromGridFs {
GridFsResources[] txtFiles = operations.getResources("*.txt");
}
}</programlisting>
</example>
<para><interfacename>GridFsOperations</interfacename> extending
<interfacename>ResourcePatternResolver</interfacename> allows the
<classname>GridFsTemplate</classname> e.g. to be plugged into an
<interfacename>ApplicationContext</interfacename> to read Spring Config
files from a MongoDB.</para>
</section>
</chapter>