DATAMONGO-1334 - Map-reduce operations now honor MapReduceOptions.limit.

We now also consider the limit set via MapReduceOptions when executing mapReduce operations via MongoTemplate.mapReduce(…).

MapReduceOptions.limit(…) supersedes a potential limit set via the Query itself. This change also allows to define a limit even when no explicit Query is used.

Original pull request: #338.

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/MongoTemplate.java

@@ -1579,8 +1579,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware {
 				throw new InvalidDataAccessApiUsageException(
 						"Can not use skip or field specification with map reduce operations");
 			}
-
-			if (query.getLimit() > 0) {
+			if (query.getLimit() > 0 && mapReduceOptions.getLimit() == null) {
 				mapReduceCommand.setLimit(query.getLimit());
 			}
 			if (query.getSortObject() != null) {
@@ -1588,6 +1587,10 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware {
 			}
 		}
 
+		if (mapReduceOptions.getLimit() != null && mapReduceOptions.getLimit().intValue() > 0) {
+			mapReduceCommand.setLimit(mapReduceOptions.getLimit());
+		}
+
 		if (mapReduceOptions.getJavaScriptMode() != null) {
 			mapReduceCommand.setJsMode(true);
 		}

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/mapreduce/MapReduceOptions.java

@@ -45,6 +45,8 @@ public class MapReduceOptions {
 
 	private Boolean verbose = true;
 
+	private Integer limit;
+
 	private Map<String, Object> extraOptions = new HashMap<String, Object>();
 
 	/**
@@ -64,6 +66,8 @@ public class MapReduceOptions {
 	 * @return MapReduceOptions so that methods can be chained in a fluent API style
 	 */
 	public MapReduceOptions limit(int limit) {
+
+		this.limit = limit;
 		return this;
 	}
 
@@ -247,6 +251,15 @@ public class MapReduceOptions {
 		return this.scopeVariables;
 	}
 
+	/**
+	 * Get the maximum number of documents for the input into the map function.
+	 * 
+	 * @return {@literal null} if not set.
+	 */
+	public Integer getLimit() {
+		return limit;
+	}
+
 	public DBObject getOptionsObject() {
 		BasicDBObject cmd = new BasicDBObject();
 
@@ -264,6 +277,10 @@ public class MapReduceOptions {
 			cmd.put("scope", scopeVariables);
 		}
 
+		if (limit != null) {
+			cmd.put("limit", limit);
+		}
+
 		if (!extraOptions.keySet().isEmpty()) {
 			cmd.putAll(extraOptions);
 		}

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/MongoTemplateUnitTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2014 the original author or authors.
+ * Copyright 2010-2015 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -52,6 +52,7 @@ import org.springframework.data.mongodb.core.convert.MappingMongoConverter;
 import org.springframework.data.mongodb.core.convert.QueryMapper;
 import org.springframework.data.mongodb.core.index.MongoPersistentEntityIndexCreator;
 import org.springframework.data.mongodb.core.mapping.MongoMappingContext;
+import org.springframework.data.mongodb.core.mapreduce.MapReduceOptions;
 import org.springframework.data.mongodb.core.query.BasicQuery;
 import org.springframework.data.mongodb.core.query.Criteria;
 import org.springframework.data.mongodb.core.query.NearQuery;
@@ -66,6 +67,8 @@ import com.mongodb.DB;
 import com.mongodb.DBCollection;
 import com.mongodb.DBCursor;
 import com.mongodb.DBObject;
+import com.mongodb.MapReduceCommand;
+import com.mongodb.MapReduceOutput;
 import com.mongodb.Mongo;
 import com.mongodb.MongoException;
 import com.mongodb.ReadPreference;
@@ -422,6 +425,112 @@ public class MongoTemplateUnitTests extends MongoOperationsUnitTests {
 		verify(this.db, times(1)).command(Mockito.any(DBObject.class));
 	}
 
+	/**
+	 * @see DATAMONGO-1334
+	 */
+	@Test
+	public void mapReduceShouldUseZeroAsDefaultLimit() {
+
+		ArgumentCaptor<MapReduceCommand> captor = ArgumentCaptor.forClass(MapReduceCommand.class);
+
+		MapReduceOutput output = mock(MapReduceOutput.class);
+		when(output.results()).thenReturn(Collections.<DBObject> emptySet());
+		when(collection.mapReduce(Mockito.any(MapReduceCommand.class))).thenReturn(output);
+
+		Query query = new BasicQuery("{'foo':'bar'}");
+
+		template.mapReduce(query, "collection", "function(){}", "function(key,values){}", Wrapper.class);
+
+		verify(collection).mapReduce(captor.capture());
+
+		assertThat(captor.getValue().getLimit(), is(0));
+	}
+
+	/**
+	 * @see DATAMONGO-1334
+	 */
+	@Test
+	public void mapReduceShouldPickUpLimitFromQuery() {
+
+		ArgumentCaptor<MapReduceCommand> captor = ArgumentCaptor.forClass(MapReduceCommand.class);
+
+		MapReduceOutput output = mock(MapReduceOutput.class);
+		when(output.results()).thenReturn(Collections.<DBObject> emptySet());
+		when(collection.mapReduce(Mockito.any(MapReduceCommand.class))).thenReturn(output);
+
+		Query query = new BasicQuery("{'foo':'bar'}");
+		query.limit(100);
+
+		template.mapReduce(query, "collection", "function(){}", "function(key,values){}", Wrapper.class);
+
+		verify(collection).mapReduce(captor.capture());
+
+		assertThat(captor.getValue().getLimit(), is(100));
+	}
+
+	/**
+	 * @see DATAMONGO-1334
+	 */
+	@Test
+	public void mapReduceShouldPickUpLimitFromOptions() {
+
+		ArgumentCaptor<MapReduceCommand> captor = ArgumentCaptor.forClass(MapReduceCommand.class);
+
+		MapReduceOutput output = mock(MapReduceOutput.class);
+		when(output.results()).thenReturn(Collections.<DBObject> emptySet());
+		when(collection.mapReduce(Mockito.any(MapReduceCommand.class))).thenReturn(output);
+
+		Query query = new BasicQuery("{'foo':'bar'}");
+
+		template.mapReduce(query, "collection", "function(){}", "function(key,values){}",
+				new MapReduceOptions().limit(1000), Wrapper.class);
+
+		verify(collection).mapReduce(captor.capture());
+		assertThat(captor.getValue().getLimit(), is(1000));
+	}
+
+	/**
+	 * @see DATAMONGO-1334
+	 */
+	@Test
+	public void mapReduceShouldPickUpLimitFromOptionsWhenQueryIsNotPresent() {
+
+		ArgumentCaptor<MapReduceCommand> captor = ArgumentCaptor.forClass(MapReduceCommand.class);
+
+		MapReduceOutput output = mock(MapReduceOutput.class);
+		when(output.results()).thenReturn(Collections.<DBObject> emptySet());
+		when(collection.mapReduce(Mockito.any(MapReduceCommand.class))).thenReturn(output);
+
+		template.mapReduce("collection", "function(){}", "function(key,values){}", new MapReduceOptions().limit(1000),
+				Wrapper.class);
+
+		verify(collection).mapReduce(captor.capture());
+		assertThat(captor.getValue().getLimit(), is(1000));
+	}
+
+	/**
+	 * @see DATAMONGO-1334
+	 */
+	@Test
+	public void mapReduceShouldPickUpLimitFromOptionsEvenWhenQueryDefinesItDifferently() {
+
+		ArgumentCaptor<MapReduceCommand> captor = ArgumentCaptor.forClass(MapReduceCommand.class);
+
+		MapReduceOutput output = mock(MapReduceOutput.class);
+		when(output.results()).thenReturn(Collections.<DBObject> emptySet());
+		when(collection.mapReduce(Mockito.any(MapReduceCommand.class))).thenReturn(output);
+
+		Query query = new BasicQuery("{'foo':'bar'}");
+		query.limit(100);
+
+		template.mapReduce(query, "collection", "function(){}", "function(key,values){}",
+				new MapReduceOptions().limit(1000), Wrapper.class);
+
+		verify(collection).mapReduce(captor.capture());
+
+		assertThat(captor.getValue().getLimit(), is(1000));
+	}
+
 	class AutogenerateableId {
 
 		@Id BigInteger id;

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/mapreduce/MapReduceOptionsTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2011 the original author or authors.
+ * Copyright 2010-2015 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -15,12 +15,40 @@
  */
 package org.springframework.data.mongodb.core.mapreduce;
 
+import static org.junit.Assert.*;
+import static org.springframework.data.mongodb.test.util.IsBsonObject.*;
+
 import org.junit.Test;
 
+/**
+ * @author Mark Pollack
+ * @author Oliver Gierke
+ * @author Christoph Strobl
+ */
 public class MapReduceOptionsTests {
 
 	@Test
 	public void testFinalize() {
 		new MapReduceOptions().finalizeFunction("code");
 	}
+
+	/**
+	 * @see DATAMONGO-1334
+	 */
+	@Test
+	public void limitShouldBeIncludedCorrectly() {
+
+		MapReduceOptions options = new MapReduceOptions();
+		options.limit(10);
+
+		assertThat(options.getOptionsObject(), isBsonObject().containing("limit", 10));
+	}
+
+	/**
+	 * @see DATAMONGO-1334
+	 */
+	@Test
+	public void limitShouldNotBePresentInDboWhenNotSet() {
+		assertThat(new MapReduceOptions().getOptionsObject(), isBsonObject().notContaining("limit"));
+	}
 }