spring-data-jpa/src/docbkx/reference/jpa.xml

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<chapter id="jpa.repositories">
  <title>JPA Repositories</title>

  <abstract>
    <para>This chapter includes details of the JPA repository
    implementation.</para>
  </abstract>

  <section id="jpa.introduction">
    <title>Introduction</title>

    <section id="jpa.namespace">
      <title>Spring namespace</title>

      <para>The JPA module of Spring Data contains a custom namespace that
      allows defining repository beans. It also contains certain features and
      element attributes that are special to JPA. Generally the JPA
      repositories can be set up using the <code>repositories</code>
      element:</para>

      <example>
        <title>Setting up JPA repositories using the namespace</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:jpa="http://www.springframework.org/schema/data/jpa"
  xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans.xsd
    http://www.springframework.org/schema/data/jpa
    http://www.springframework.org/schema/data/jpa/spring-jpa.xsd"&gt;

  &lt;jpa:repositories base-package="com.acme.repositories" /&gt;

&lt;/beans&gt;</programlisting>
      </example>

      <para>Using this element looks up Spring Data repositories as described
      in <xref linkend="repositories.create-instances"/>. Beyond that it
      activates persistence exception translation for all beans annotated with
      <interfacename>@Repository</interfacename> to let exceptions being
      thrown by the JPA presistence providers be converted into Spring's
      <classname>DataAccessException</classname> hierarchy.</para>

      <simplesect id="jpa.namespace-attributes">
        <title>Custom namespace attributes</title>

        <para>Beyond the default attributes of the <code>repositories</code>
        element the JPA namespace offers additional attributes to gain more
        detailled control over the setup of the repositories:</para>

        <table>
          <title>Custom JPA-specific attributes of the repositories
          element</title>

          <tgroup cols="2">
            <tbody>
              <row>
                <entry><code>entity-manager-factory-ref</code></entry>

                <entry>Explicitly wire the
                <interfacename>EntityManagerFactory</interfacename> to be used
                with the repositories being detected by the
                <code>repositories</code> element. Usually used if multiple
                <interfacename>EntityManagerFactory</interfacename> beans are
                used within the application. If not configured we will
                automatically lookup the single
                <interfacename>EntityManagerFactory</interfacename> configured
                in the
                <interfacename>ApplicationContext</interfacename>.</entry>
              </row>

              <row>
                <entry><code>transaction-manager-ref</code></entry>

                <entry>Explicitly wire the
                <interfacename>PlatformTransactionManager</interfacename> to
                be used with the repositories being detected by the
                <code>repositories</code> element. Usually only necessary if
                multiple transaction managers and/or
                <interfacename>EntityManagerFactory</interfacename> beans have
                been configured. Default to a single defined
                <interfacename>PlatformTransactionManager</interfacename>
                inside the current
                <interfacename>ApplicationContext</interfacename>.</entry>
              </row>
            </tbody>
          </tgroup>
        </table>
      </simplesect>
    </section>
  </section>

  <section id="jpa.query-methods">
    <title>Query methods</title>

    <section id="jpa.sample-app.finders.strategies">
      <title>Query lookup strategies</title>

      <para>The JPA module supports defining a query manually as String or
      have it being derived from the method name.</para>

      <simplesect>
        <title>Declared queries</title>

        <para>Although getting a query derived from the method name is quite
        convenient, one might face the situation in which either the method
        name parser does not support the keyword one wants to use or the
        method name would get unnecessarily ugly. So you can either use JPA
        named queries through a naming convention (see <xref
        linkend="jpa.query-methods.named-queries"/> for more information) or
        rather annotate your query method with
        <interfacename>@Query</interfacename> (see <xref
        linkend="jpa.query-methods.at-query"/> for details).</para>
      </simplesect>
    </section>

    <section id="jpa.query-methods.query-creation">
      <title>Query creation</title>

      <para>Generally the query creation mechanism for JPA works as described
      in <xref linkend="repositories.query-methods"/>. Here's a short example
      of what a JPA query method translates into:<example>
          <title>Query creation from method names</title>

          <para><programlisting language="java">public interface UserRepository extends Repository&lt;User, Long&gt; {

  List&lt;User&gt; findByEmailAddressAndLastname(String emailAddress, String lastname);
}</programlisting>We will create a query using the JPA criteria API from this
          but essentially this translates into the following query:</para>

          <programlisting>select u from User u where u.emailAddress = ?1 and u.lastname = ?2</programlisting>

          <para>Spring Data JPA will do a property check and traverse nested
          properties as described in <xref
          linkend="repositories.query-methods.property-expressions"/>. Here's
          an overview of the keywords supported for JPA and what a method
          containing that keyword essentially translates to.</para>
        </example></para>

      <para><table>
          <title>Supported keywords inside method names</title>

          <tgroup cols="3">
            <colspec colwidth="1*"/>

            <colspec colwidth="2*"/>

            <colspec colwidth="3*"/>

            <thead>
              <row>
                <entry>Keyword</entry>

                <entry>Sample</entry>

                <entry>JPQL snippet</entry>
              </row>
            </thead>

            <tbody>
              <row>
                <entry><code>And</code></entry>

                <entry><code>findByLastnameAndFirstname</code></entry>

                <entry><code>… where x.lastname = ?1 and x.firstname =
                ?2</code></entry>
              </row>

              <row>
                <entry><code>Or</code></entry>

                <entry><code>findByLastnameOrFirstname</code></entry>

                <entry><code>… where x.lastname = ?1 or x.firstname =
                ?2</code></entry>
              </row>

              <row>
                <entry><code>Between</code></entry>

                <entry><code>findByStartDateBetween</code></entry>

                <entry><code>… where x.startDate between 1? and
                ?2</code></entry>
              </row>

              <row>
                <entry><code>LessThan</code></entry>

                <entry><code>findByAgeLessThan</code></entry>

                <entry><code>… where x.age &lt; ?1</code></entry>
              </row>

              <row>
                <entry><code>GreaterThan</code></entry>

                <entry><code>findByAgeGreaterThan</code></entry>

                <entry><code>… where x.age &gt; ?1</code></entry>
              </row>

              <row>
                <entry><code>After</code></entry>

                <entry><code>findByStartDateAfter</code></entry>

                <entry><code>… where x.startDate &gt; ?1</code></entry>
              </row>

              <row>
                <entry><code>Before</code></entry>

                <entry><code>findByStartDateBefore</code></entry>

                <entry><code>… where x.startDate &lt; ?1</code></entry>
              </row>

              <row>
                <entry><code>IsNull</code></entry>

                <entry><code>findByAgeIsNull</code></entry>

                <entry><code>… where x.age is null</code></entry>
              </row>

              <row>
                <entry><code>IsNotNull,NotNull</code></entry>

                <entry><code>findByAge(Is)NotNull</code></entry>

                <entry><code>… where x.age not null</code></entry>
              </row>

              <row>
                <entry><code>Like</code></entry>

                <entry><code>findByFirstnameLike</code></entry>

                <entry><code>… where x.firstname like ?1</code></entry>
              </row>

              <row>
                <entry><code>NotLike</code></entry>

                <entry><code>findByFirstnameNotLike</code></entry>

                <entry><code>… where x.firstname not like ?1</code></entry>
              </row>

              <row>
                <entry><code>StartingWith</code></entry>

                <entry><code>findByFirstnameStartingWith</code></entry>

                <entry><code>… where x.firstname like ?1</code> (parameter
                bound with prepended <code>%</code>)</entry>
              </row>

              <row>
                <entry><code>ngWith</code></entry>

                <entry><code>findByFirstnameEndingWith</code></entry>

                <entry><code>… where x.firstname like ?1</code> (parameter
                bound with appended <code>%</code>)</entry>
              </row>

              <row>
                <entry><code>Containing</code></entry>

                <entry><code>findByFirstnameContaining</code></entry>

                <entry><code>… where x.firstname like ?1</code> (parameter
                bound wrapped in <code>%</code>)</entry>
              </row>

              <row>
                <entry><code>OrderBy</code></entry>

                <entry><code>findByAgeOrderByLastnameDesc</code></entry>

                <entry><code>… where x.age = ?1 order by x.lastname
                desc</code></entry>
              </row>

              <row>
                <entry><code>Not</code></entry>

                <entry><code>findByLastnameNot</code></entry>

                <entry><code>… where x.lastname &lt;&gt; ?1</code></entry>
              </row>

              <row>
                <entry><code>In</code></entry>

                <entry><code>findByAgeIn(Collection&lt;Age&gt;
                ages)</code></entry>

                <entry><code>… where x.age in ?1</code></entry>
              </row>

              <row>
                <entry><code>NotIn</code></entry>

                <entry><code>findByAgeNotIn(Collection&lt;Age&gt;
                age)</code></entry>

                <entry><code>… where x.age not in ?1</code></entry>
              </row>

              <row>
                <entry><code>True</code></entry>

                <entry><code>findByActiveTrue()</code></entry>

                <entry><code>… where x.active = true</code></entry>
              </row>

              <row>
                <entry><code>False</code></entry>

                <entry><code>findByActiveFalse()</code></entry>

                <entry><code>… where x.active = false</code></entry>
              </row>
            </tbody>
          </tgroup>
        </table><note>
          <para><code>In</code> and <code>NotIn</code> also take any subclass
          of <interfacename>Collection</interfacename> as parameter as well as
          arrays or varargs. For other syntactical versions of the very same
          logical operator check <xref
          linkend="repository-query-keywords"/>.</para>
        </note></para>
    </section>

    <section id="jpa.query-methods.named-queries">
      <title>Using JPA NamedQueries</title>

      <note>
        <para>The examples use simple <code>&lt;named-query /&gt;</code>
        element and <code>@NamedQuery</code> annotation. The queries for these
        configuration elements have to be defined in JPA query language. Of
        course you can use <code>&lt;named-native-query /&gt;</code> or
        <code>@NamedNativeQuery</code> too. These elements allow you to define
        the query in native SQL by losing the database platform
        independence.</para>
      </note>

      <simplesect>
        <title>XML named query definition</title>

        <para>To use XML configuration simply add the necessary
        <code>&lt;named-query /&gt;</code> element to the
        <filename>orm.xml</filename> JPA configuration file located in
        <filename>META-INF</filename> folder of your classpath. Automatic
        invocation of named queries is enabled by using some defined naming
        convention. For more details see below.</para>

        <example>
          <title>XML named query configuration</title>

          <programlisting language="xml">&lt;named-query name="User.findByLastname"&gt;
  &lt;query&gt;select u from User u where u.lastname = ?1&lt;/query&gt;
&lt;/named-query&gt;</programlisting>
        </example>

        <para>As you can see the query has a special name which will be used
        to resolve it at runtime.</para>
      </simplesect>

      <simplesect>
        <title>Annotation configuration</title>

        <para>Annotation configuration has the advantage of not needing
        another configuration file to be edited, probably lowering maintenance
        costs. You pay for that benefit by the need to recompile your domain
        class for every new query declaration.</para>

        <example>
          <title>Annotation based named query configuration</title>

          <programlisting language="java">@Entity
@NamedQuery(name = "User.findByEmailAddress",
  query = "select u from User u where u.emailAddress = ?1")
public class User {

}</programlisting>
        </example>
      </simplesect>

      <simplesect>
        <title>Declaring interfaces</title>

        <para>To allow execution of these named queries all you need to do is
        to specify the <interfacename>UserRepository</interfacename> as
        follows:</para>

        <example>
          <title>Query method declaration in UserRepository</title>

          <programlisting language="java">public interface UserRepository extends JpaRepository&lt;User, Long&gt; {

  List&lt;User&gt; findByLastname(String lastname);

  User findByEmailAddress(String emailAddress);
}</programlisting>
        </example>

        <para>Spring Data will try to resolve a call to these methods to a
        named query, starting with the simple name of the configured domain
        class, followed by the method name separated by a dot. So the example
        here would use the named queries defined above instead of trying to
        create a query from the method name.</para>
      </simplesect>
    </section>

    <section id="jpa.query-methods.at-query">
      <title>Using @Query</title>

      <para>Using named queries to declare queries for entities is a valid
      approach and works fine for a small number of queries. As the queries
      themselves are tied to the Java method that executes them you actually
      can bind them directly using the Spring Data JPA <code>@Query</code>
      annotation rather than annotating them to the domain class. This will
      free the domain class from persistence specific information and
      co-locate the query to the repository interface.</para>

      <para>Queries annotated to the query method will take precedence over
      queries defined using <code>@NamedQuery</code> or named queries declared
      in <filename>orm.xml</filename>.</para>

      <example>
        <title>Declare query at the query method using @Query</title>

        <programlisting language="java">public interface UserRepository extends JpaRepository&lt;User, Long&gt; {

  @Query("select u from User u where u.emailAddress = ?1")
  User findByEmailAddress(String emailAddress);
}</programlisting>
      </example>

      <simplesect>
        <title>Native queries</title>

        <para>The <interfacename>@Query</interfacename> annotation allows to
        execute native queries by setting the <code>nativeQuery</code> flag to
        true. Note, that we currently don't support execution of pagination or
        dynamic sorting for native queries as we'd have to manipulate the
        actual query declared and we cannot do this reliably for native
        SQL.</para>
      </simplesect>
    </section>

    <section id="jpa.named-parameters">
      <title>Using named parameters</title>

      <para>By default Spring Data JPA will use position based parameter
      binding as described in all the samples above. This makes query methods
      a little error prone to refactoring regarding the parameter position. To
      solve this issue you can use <code>@Param</code> annotation to give a
      method parameter a concrete name and bind the name in the query:</para>

      <example>
        <title>Using named parameters</title>

        <programlisting language="java">public interface UserRepository extends JpaRepository&lt;User, Long&gt; {

  @Query("select u from User u where u.firstname = :firstname or u.lastname = :lastname")
  User findByLastnameOrFirstname(@Param("lastname") String lastname,
                                 @Param("firstname") String firstname);
}</programlisting>

        <para>Note that the method parameters are switched according to the
        occurrence in the query defined.</para>
      </example>
    </section>

    <section id="jpa.modifying-queries">
      <title>Modifying queries</title>

      <para>All the sections above describe how to declare queries to access a
      given entity or collection of entities. Of course you can add custom
      modifying behaviour by using facilities described in <xref
      linkend="repositories.custom-implementations"/>. As this approach is
      feasible for comprehensive custom functionality, you can achieve the
      execution of modifying queries that actually only need parameter binding
      by annotating the query method with <code>@Modifying</code>:</para>

      <example>
        <title>Declaring manipulating queries</title>

        <programlisting language="java">@Modifying
@Query("update User u set u.firstname = ?1 where u.lastname = ?2")
int setFixedFirstnameFor(String firstname, String lastname);</programlisting>
      </example>

      <para>This will trigger the query annotated to the method as updating
      query instead of a selecting one. As the
      <interfacename>EntityManager</interfacename> might contain outdated
      entities after the execution of the modifying query, we automatically
      clear it (see JavaDoc of
      <interfacename>EntityManager</interfacename>.<methodname>clear()</methodname>
      for details). This will effectively drop all non-flushed changes still
      pending in the <interfacename>EntityManager</interfacename>. If you
      don't wish the <interfacename>EntityManager</interfacename> to be
      cleared automatically you can set
      <interfacename>@Modifying</interfacename> annotation's
      <code>clearAutomatically</code> attribute to
      <literal>false</literal>;</para>
    </section>

    <section id="jpa.query-hints">
      <title>Applying query hints</title>

      <para>To apply JPA <interfacename>QueryHint</interfacename>s to the
      queries declared in your repository interface you can use the
      <interfacename>QueryHints</interfacename> annotation. It takes an array
      of JPA <interfacename>QueryHint</interfacename> annotations plus a
      boolean flag to potentially disable the hints applied to the addtional
      count query triggered when applying pagination.</para>

      <example>
        <title>Using QueryHints with a repository method</title>

        <programlisting language="java">public interface UserRepository extends Repository&lt;User, Long&gt; {

  @QueryHints(value = { @QueryHint(name = "name", value = "value")}, 
              forCounting = false)
  Page&lt;User&gt; findByLastname(String lastname, Pageable pageable);
}</programlisting>

        <para>The just shown declaration would apply the configured
        <interfacename>QueryHint</interfacename> for that actually query but
        omit applying it to the count query triggered to calculate the total
        number of pages.</para>
      </example>
    </section>
  </section>

  <section id="specifications">
    <title>Specifications</title>

    <para>JPA 2 introduces a criteria API that can be used to build queries
    programmatically. Writing a <code>criteria</code> you actually define the
    where-clause of a query for a domain class. Taking another step back these
    criteria can be regarded as predicate over the entity that is described by
    the JPA criteria API constraints.</para>

    <para>Spring Data JPA takes the concept of a specification from Eric
    Evans' book "Domain Driven Design", following the same semantics and
    providing an API to define such
    <interfacename>Specification</interfacename>s using the JPA criteria API.
    To support specifications you can extend your repository interface with
    the <interfacename>JpaSpecificationExecutor</interfacename>
    interface:</para>

    <programlisting language="java">public interface CustomerRepository extends CrudRepository&lt;Customer, Long&gt;, JpaSpecificationExecutor {
 …
}</programlisting>

    <para>The additional interface carries methods that allow you to execute
    <interfacename>Specification</interfacename>s in a variety of ways.</para>

    <para>For example, the <code>readAll</code> method will return all
    entities that match the specification: </para>

    <programlisting language="java">List&lt;T&gt; readAll(Specification&lt;T&gt; spec);</programlisting>

    <para>The <interfacename>Specification</interfacename> interface is as
    follows:</para>

    <programlisting language="java">public interface Specification&lt;T&gt; {
  Predicate toPredicate(Root&lt;T&gt; root, CriteriaQuery&lt;?&gt; query,
            CriteriaBuilder builder);
}</programlisting>

    <para>Okay, so what is the typical use case?
    <interfacename>Specification</interfacename>s can easily be used to build
    an extensible set of predicates on top of an entity that then can be
    combined and used with <interfacename>JpaRepository</interfacename>
    without the need to declare a query (method) for every needed combination.
    Here's an example:</para>

    <example>
      <title>Specifications for a Customer</title>

      <programlisting language="java">public class CustomerSpecs {

  public static Specification&lt;Customer&gt; isLongTermCustomer() {
    return new Specification&lt;Customer&gt;() {
      Predicate toPredicate(Root&lt;T&gt; root, CriteriaQuery&lt;?&gt; query,
            CriteriaBuilder builder) {

         LocalDate date = new LocalDate().minusYears(2);
         return builder.lessThan(root.get(Customer_.createdAt), date);
      }
    };
  }

  public static Specification&lt;Customer&gt; hasSalesOfMoreThan(MontaryAmount value) {
    return new Specification&lt;Customer&gt;() {
      Predicate toPredicate(Root&lt;T&gt; root, CriteriaQuery&lt;?&gt; query,
            CriteriaBuilder builder) {

         // build query here
      }
    };
  }
}</programlisting>
    </example>

    <para>Admittedly the amount of boilerplate leaves room for improvement
    (that will hopefully be reduced by Java 8 closures) but the client side
    becomes much nicer as you will see below. Besides that we have expressed
    some criteria on a business requirement abstraction level and created
    executable <interfacename>Specification</interfacename>s. So a client
    might use a <interfacename>Specification</interfacename> as
    follows:</para>

    <example>
      <title>Using a simple Specification</title>

      <programlisting language="java">List&lt;Customer&gt; customers = customerRepository.findAll(isLongTermCustomer());</programlisting>
    </example>

    <para>Okay, why not simply create a query for this kind of data access?
    You're right. Using a single <interfacename>Specification</interfacename>
    does not gain a lot of benefit over a plain query declaration. The power
    of <interfacename>Specification</interfacename>s really shines when you
    combine them to create new <interfacename>Specification</interfacename>
    objects. You can achieve this through the
    <classname>Specifications</classname> helper class we provide to build
    expressions like this:</para>

    <example>
      <title>Combined Specifications</title>

      <para><programlisting language="java">MonetaryAmount amount = new MonetaryAmount(200.0, Currencies.DOLLAR);
List&lt;Customer&gt; customers = customerRepository.readAll(
  where(isLongTermCustomer()).or(hasSalesOfMoreThan(amount)));</programlisting>As
      you can see, <classname>Specifications</classname> offers some glue-code
      methods to chain and combine
      <interfacename>Specification</interfacename>s. Thus extending your data
      access layer is just a matter of creating new
      <interfacename>Specification</interfacename> implementations and
      combining them with ones already existing.</para>
    </example>
  </section>

  <section id="transactions">
    <title>Transactionality</title>

    <para>CRUD methods on repository instances are transactional by default.
    For reading operations the transaction configuration <code>readOnly</code>
    flag is set to true, all others are configured with a plain
    <classname>@Transactional</classname> so that default transaction
    configuration applies. For details see JavaDoc of
    <classname>Repository</classname>. If you need to tweak transaction
    configuration for one of the methods declared in
    <interfacename>Repository</interfacename> simply redeclare the method in
    your repository interface as follows:</para>

    <example>
      <title>Custom transaction configuration for CRUD</title>

      <programlisting language="java">public interface UserRepository extends JpaRepository&lt;User, Long&gt; {

  @Override
  @Transactional(timeout = 10)
  public List&lt;User&gt; findAll();

  // Further query method declarations
}</programlisting>

      <para>This will cause the <methodname>findAll()</methodname> method to
      be executed with a timeout of 10 seconds and without the
      <code>readOnly</code> flag.</para>
    </example>

    <para>Another possibility to alter transactional behaviour is using a
    facade or service implementation that typically covers more than one
    repository. Its purpose is to define transactional boundaries for non-CRUD
    operations:</para>

    <example>
      <title>Using a facade to define transactions for multiple repository
      calls</title>

      <programlisting language="java">@Service
class UserManagementImpl implements UserManagement {

  private final UserRepository userRepository;
  private final RoleRepository roleRepository;

  @Autowired
  public UserManagementImpl(UserRepository userRepository,
    RoleRepository roleRepository) {
    this.userRepository = userRepository;
    this.roleRepository = roleRepository;
  }

  @Transactional
  public void addRoleToAllUsers(String roleName) {

    Role role = roleRepository.findByName(roleName);

    for (User user : userRepository.readAll()) {
      user.addRole(role);
      userRepository.save(user);
    }
}</programlisting>

      <para>This will cause call to
      <methodname>addRoleToAllUsers(…)</methodname> to run inside a
      transaction (participating in an existing one or create a new one if
      none already running). The transaction configuration at the repositories
      will be neglected then as the outer transaction configuration determines
      the actual one used. Note that you will have to activate
      <code>&lt;tx:annotation-driven /&gt;</code> explicitly to get annotation
      based configuration at facades working. The example above assumes you
      are using component scanning.</para>
    </example>

    <section id="transactional-query-methods">
      <title>Transactional query methods</title>

      <para>To allow your query methods to be transactional simply use
      <interfacename>@Transactional</interfacename> at the repository
      interface you define.</para>

      <example>
        <title>Using @Transactional at query methods</title>

        <programlisting language="java">@Transactional(readOnly = true)
public interface UserRepository extends JpaRepository&lt;User, Long&gt; {

  List&lt;User&gt; findByLastname(String lastname);

  @Modifying
  @Transactional
  @Query("delete from User u where u.active = false")
  void deleteInactiveUsers();
}</programlisting>

        <para>Typically you will want the <code>readOnly</code> flag set to
        true as most of the query methods will only read data. In contrast to
        that <methodname>deleteInactiveUsers()</methodname> makes use of the
        <interfacename>@Modifying</interfacename> annotation and overrides the
        transaction configuration. Thus the method will be executed with
        <code>readOnly</code> flag set to false.</para>
      </example>

      <note>
        <para>It's definitely reasonable to use transactions for read only
        queries and we can mark them as such by setting the
        <code>readOnly</code> flag. This will not, however, act as check that
        you do not trigger a manipulating query (although some databases
        reject <literal>INSERT</literal> and <literal>UPDATE</literal>
        statements inside a read only transaction). The <code>readOnly</code>
        flag instead is propagated as hint to the underlying JDBC driver for
        performance optimizations. Furthermore, Spring will perform some
        optimizations on the underlying JPA provider. E.g. when used with
        Hibernate the flush mode is set to <code>NEVER</code> when you
        configure a transaction as <code>readOnly</code> which causes
        Hibernate to skip dirty checks (a noticeable improvement on large
        object trees).</para>
      </note>
    </section>
  </section>

  <section id="locking">
    <title>Locking</title>

    <para>To specify the lock mode to be used the
    <interfacename>@Lock</interfacename> annotation can be used on query
    methods:</para>

    <example>
      <title>Defining lock metadata on query methods</title>

      <programlisting language="java">interface UserRepository extends Repository&lt;User, Long&gt; {

  // Plain query method
  @Lock(LockModeType.READ)
  List&lt;User&gt; findByLastname(String lastname);
}</programlisting>
    </example>

    <para>This method declaration will cause the query being triggered to be
    equipped with the <interfacename>LockModeType</interfacename>
    <code>READ</code>. You can also define locking for CRUD methods by
    redeclaring them in your repository interface and adding the
    <interfacename>@Lock</interfacename> annotation:</para>

    <example>
      <title>Defining lock metadata on CRUD methods</title>

      <programlisting language="java">interface UserRepository extends Repository&lt;User, Long&gt; {

  // Redeclaration of a CRUD method
  @Lock(LockModeType.READ);
  List&lt;User&gt; findAll();
}</programlisting>
    </example>
  </section>

  <section id="jpa.auditing">
    <title>Auditing</title>

    <para>Most applications will require some form of auditability to track
    when an entity was created or modified and by whom. Spring Data JPA
    provides facilities to add this audit information to an entity
    transparently by AOP means. To take part in this functionality your domain
    classes must implement a more advanced interface:</para>

    <example>
      <title><interfacename>Auditable</interfacename> interface</title>

      <programlisting language="java">public interface Auditable&lt;U, ID extends Serializable&gt;
        extends Persistable&lt;ID&gt; {

    U getCreatedBy();

    void setCreatedBy(U createdBy);

    DateTime getCreatedDate();

    void setCreated(Date creationDate);

    U getLastModifiedBy();

    void setLastModifiedBy(U lastModifiedBy);

    DateTime getLastModifiedDate();

    void setLastModified(Date lastModifiedDate);
}</programlisting>
    </example>

    <para>As you can see the modifying entity itself only has to be an entity.
    Mostly this will be some sort of User entity, so we chose U as parameter
    type.</para>

    <note>
      <para>To minimize boilerplate code Spring Data JPA offers
      <classname>AbstractPersistable</classname> and
      <classname>AbstractAuditable</classname> base classes that implement and
      pre-configure entities. Thus you can decide to only implement the
      interface or enjoy more sophisticated support by extending the base
      class.</para>
    </note>

    <simplesect>
      <title>General auditing configuration</title>

      <para>Spring Data JPA ships with an entity listener that can be used to
      trigger capturing auditing information. So first you have to register
      the <classname>AuditingEntityListener</classname> inside your
      <filename>orm.xml</filename> to be used for all entities in your
      persistence contexts:</para>

      <example>
        <title>Auditing configuration orm.xml</title>

        <programlisting language="xml">&lt;persistence-unit-metadata&gt;
  &lt;persistence-unit-defaults&gt;
    &lt;entity-listeners&gt;
      &lt;entity-listener class="….data.jpa.domain.support.AuditingEntityListener" /&gt;
    &lt;/entity-listeners&gt;
  &lt;/persistence-unit-defaults&gt;
&lt;/persistence-unit-metadata&gt;</programlisting>
      </example>

      <para>Now activating auditing functionality is just a matter of adding
      the Spring Data JPA <literal>auditing</literal> namespace element to
      your configuration:</para>

      <example>
        <title>Activating auditing in the Spring configuration</title>

        <programlisting language="xml">&lt;jpa:auditing auditor-aware-ref="yourAuditorAwareBean" /&gt;</programlisting>
      </example>

      <para>As you can see you have to provide a bean that implements the
      <interfacename>AuditorAware</interfacename> interface which looks as
      follows:</para>

      <example>
        <title><interfacename>AuditorAware</interfacename> interface</title>

        <programlisting language="java">public interface AuditorAware&lt;T, ID extends Serializable&gt; {

    T getCurrentAuditor();
}</programlisting>
      </example>

      <para>Usually you will have some kind of authentication component in
      your application that tracks the user currently working with the system.
      This component should be <interfacename>AuditorAware</interfacename> and
      thus allow seamless tracking of the auditor.</para>
    </simplesect>
  </section>

  <section id="jpa.misc">
    <title>Miscellaneous</title>

    <section id="jpa.misc.merging-persistence-units">
      <title>Merging persistence units</title>

      <para>Spring supports having multiple persistence units out of the box.
      Sometimes, however, you might want to modularize your application but
      still make sure that all these modules run inside a single persistence
      unit at runtime. To do so Spring Data JPA offers a
      <code>PersistenceUnitManager</code> implementation that automatically
      merges persistence units based on their name.</para>

      <example>
        <title>Using MergingPersistenceUnitmanager</title>

        <para><programlisting language="xml">&lt;bean class="….LocalContainerEntityManagerFactoryBean"&gt;
  &lt;property name="persistenceUnitManager"&gt;
    &lt;bean class="….MergingPersistenceUnitManager" /&gt;
  &lt;/property
&lt;/bean&gt;</programlisting></para>
      </example>
    </section>

    <section id="jpa.misc.entity-scanning">
      <title>Classpath scanning for @Entity classes and JPA mapping
      files</title>

      <para>A plain JPA setup requires all annotation mapped entity classes
      listed in <filename>orm.xml</filename>. Same applies to XML mapping
      files. Spring Data JPA provides a
      <classname>ClasspathScanningPersistenceUnitPostProcessor</classname>
      that gets a base package configured and optionally takes a mapping
      filename pattern. It will then scan the given package for classes
      annotated with <interfacename>@Entity</interfacename> or
      <interfacename>@MappedSuperclass</interfacename> and also loads the
      configuration files matching the filename pattern and hands them to the
      JPA configuration. The PostProcessor has to be configured like
      this</para>

      <example>
        <title>Using ClasspathScanningPersistenceUnitPostProcessor</title>

        <para><programlisting language="xml">&lt;bean class="….LocalContainerEntityManagerFactoryBean"&gt;
  &lt;property name="persistenceUnitPostProcessors"&gt;
    &lt;list&gt;
      &lt;bean class="org.springframework.data.jpa.support.ClasspathScanningPersistenceUnitPostProcessor"&gt;
        &lt;constructor-arg value="com.acme.domain" /&gt;
        &lt;property name="mappingFileNamePattern" value="**/*Mapping.xml" /&gt;
      &lt;/bean&gt;
    &lt;/list&gt;
  &lt;/property&gt;
&lt;/bean&gt;</programlisting></para>
      </example>

      <note>
        <para>As of Spring 3.1 a package to scan can be configured on the
        <classname>LocalContainerEntityManagerFactoryBean</classname> directly
        to enable classpath scanning for entity classes. See the <ulink
        url="http://static.springsource.org/spring/docs/3.1.x/javadoc-api/org/springframework/orm/jpa/LocalContainerEntityManagerFactoryBean.html#setPackagesToScan(java.lang.String...)">JavaDoc</ulink>
        for details.</para>
      </note>
    </section>

    <section id="jpd.misc.cdi-integration">
      <title>CDI integration</title>

      <para>Instances of the repository interfaces are usually created by a
      container, which Spring is the most natural choice when working with
      Spring Data. There's sophisticated support to easily set up Spring to
      create bean instances documented in <xref
      linkend="repositories.create-instances"/>. As of version 1.1.0 Spring
      Data JPA ships with a custom CDI extension that allows using the
      repository abstraction in CDI environments. The extension is part of the
      JAR so all you need to do to activate it is dropping the Spring Data JPA
      JAR into your classpath.</para>

      <para>You can now set up the infrastructure by implementing a CDI
      <interfacename>Producer</interfacename> for the
      <classname>EntityManagerFactory</classname>:</para>

      <programlisting language="java">class EntityManagerFactoryProducer {

  @Produces
  @ApplicationScoped
  public EntityManagerFactory createEntityManagerFactory() {
    return Persistence.createEntityManagerFactory("my-presistence-unit");
  }

  public void close(@Disposes EntityManagerFactory entityManagerFactory) {
    entityManagerFactory.close();
  }
}</programlisting>

      <para>The Spring Data JPA CDI extension will pick up all
      <interfacename>EntityManager</interfacename>s availables as CDI beans
      and create a proxy for a Spring Data repository whenever an bean of a
      repository type is requested by the container. Thus obtaining an
      instance of a Spring Data repository is a matter of declaring an
      <interfacename>@Inject</interfacename>ed property:</para>

      <programlisting language="java">class RepositoryClient {

  @Inject
  PersonRepository repository;

  public void businessMethod() {

    List&lt;Person&gt; people = repository.findAll();
  }
}</programlisting>
    </section>
  </section>
</chapter>