DATAMONGO-950 - Add support for limiting the query result in the query derivation mechanism.

When deriving the query from its method name we check for the limit set on the PartTree to pass this on to the created query. PagedExecution not takes the overall limit into account, skips a query execution entirely (if the Pageable is out of scope completely) or alters the query limits accordingly.

Note, that there has been significant rework of this compared to the pull request to avoid new API in Query and extensive changes in MongoTemplate's QueryCursorPreparer.

Original pull request: #191.

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/repository/query/AbstractMongoQuery.java

@@ -15,6 +15,7 @@
  */
 package org.springframework.data.mongodb.repository.query;
 
+import java.util.Collections;
 import java.util.List;
 
 import org.springframework.core.convert.ConversionService;
@@ -254,10 +255,26 @@ public abstract class AbstractMongoQuery implements RepositoryQuery {
 		Object execute(Query query) {
 
 			MongoEntityMetadata<?> metadata = method.getEntityInformation();
+
+			int overallLimit = query.getLimit();
 			long count = operations.count(query, metadata.getCollectionName());
+			count = overallLimit != 0 ? Math.min(count, query.getLimit()) : count;
 
-			List<?> result = operations.find(query.with(pageable), metadata.getJavaType(), metadata.getCollectionName());
+			boolean pageableOutOfScope = pageable.getOffset() > query.getLimit();
 
+			if (pageableOutOfScope) {
+				return new PageImpl<Object>(Collections.emptyList(), pageable, count);
+			}
+
+			// Apply raw pagination
+			query = query.with(pageable);
+
+			// Adjust limit if page would exceed the overall limit
+			if (overallLimit != 0 && pageable.getOffset() + pageable.getPageSize() > overallLimit) {
+				query.limit(overallLimit - pageable.getOffset());
+			}
+
+			List<?> result = operations.find(query, metadata.getJavaType(), metadata.getCollectionName());
 			return new PageImpl(result, pageable, count);
 		}
 	}

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/repository/query/PartTreeMongoQuery.java

@@ -73,6 +73,10 @@ public class PartTreeMongoQuery extends AbstractMongoQuery {
 		MongoQueryCreator creator = new MongoQueryCreator(tree, accessor, context, isGeoNearQuery);
 		Query query = creator.createQuery();
 
+		if (tree.isLimiting()) {
+			query.limit(tree.getMaxResults());
+		}
+
 		String fieldSpec = this.getQueryMethod().getFieldSpecification();
 
 		if (!StringUtils.hasText(fieldSpec)) {

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/repository/AbstractPersonRepositoryIntegrationTests.java

@@ -917,5 +917,54 @@ public abstract class AbstractPersonRepositoryIntegrationTests {
 		assertThat(result.getContent(), hasSize(2));
 		assertThat(result.getTotalPages(), is(2));
 		assertThat(result.getTotalElements(), is(3L));
+
+	}
+
+	/**
+	 * @see DATAMONGO-950
+	 */
+	@Test
+	public void shouldLimitCollectionQueryToMaxResultsWhenPresent() {
+
+		repository.save(Arrays.asList(new Person("Bob-1", "Dylan"), new Person("Bob-2", "Dylan"), new Person("Bob-3",
+				"Dylan"), new Person("Bob-4", "Dylan"), new Person("Bob-5", "Dylan")));
+		List<Person> result = repository.findTop3ByLastnameStartingWith("Dylan");
+		assertThat(result.size(), is(3));
+	}
+
+	/**
+	 * @see DATAMONGO-950
+	 */
+	@Test
+	public void shouldNotLimitPagedQueryWhenPageRequestWithinBounds() {
+
+		repository.save(Arrays.asList(new Person("Bob-1", "Dylan"), new Person("Bob-2", "Dylan"), new Person("Bob-3",
+				"Dylan"), new Person("Bob-4", "Dylan"), new Person("Bob-5", "Dylan")));
+		Page<Person> result = repository.findTop3ByLastnameStartingWith("Dylan", new PageRequest(0, 2));
+		assertThat(result.getContent().size(), is(2));
+	}
+
+	/**
+	 * @see DATAMONGO-950
+	 */
+	@Test
+	public void shouldLimitPagedQueryWhenPageRequestExceedsUpperBoundary() {
+
+		repository.save(Arrays.asList(new Person("Bob-1", "Dylan"), new Person("Bob-2", "Dylan"), new Person("Bob-3",
+				"Dylan"), new Person("Bob-4", "Dylan"), new Person("Bob-5", "Dylan")));
+		Page<Person> result = repository.findTop3ByLastnameStartingWith("Dylan", new PageRequest(1, 2));
+		assertThat(result.getContent().size(), is(1));
+	}
+
+	/**
+	 * @see DATAMONGO-950
+	 */
+	@Test
+	public void shouldReturnEmptyWhenPageRequestedPageIsTotallyOutOfScopeForLimit() {
+
+		repository.save(Arrays.asList(new Person("Bob-1", "Dylan"), new Person("Bob-2", "Dylan"), new Person("Bob-3",
+				"Dylan"), new Person("Bob-4", "Dylan"), new Person("Bob-5", "Dylan")));
+		Page<Person> result = repository.findTop3ByLastnameStartingWith("Dylan", new PageRequest(2, 2));
+		assertThat(result.getContent().size(), is(0));
 	}
 }

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/repository/PersonRepository.java

@@ -302,4 +302,15 @@ public interface PersonRepository extends MongoRepository<Person, String>, Query
 	 */
 	@Query("{lastname:?0, address.street:{$in:?1}}")
 	Page<Person> findByCustomQueryLastnameAndAddressStreetInList(String lastname, List<String> streetNames, Pageable page);
+
+	/**
+	 * @see DATAMONGO-950
+	 */
+	List<Person> findTop3ByLastnameStartingWith(String lastname);
+
+	/**
+	 * @see DATAMONGO-950
+	 */
+	Page<Person> findTop3ByLastnameStartingWith(String lastname, Pageable pageRequest);
+
 }