DATAMONGO-680, DATAMONGO-681 - Expose MongoOperations.exists(…).

We're now exposing dedicated exists(…) methods on MongoOperations which simply looks up a cursor and inspects it for the presence of at least one element. SimpleMongoRepository implementation now also uses this optimized exists check.

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

@@ -412,6 +412,12 @@ public interface MongoOperations {
 	 */
 	<T> T findOne(Query query, Class<T> entityClass, String collectionName);
 
+	boolean exists(Query query, String collectionName);
+
+	boolean exists(Query query, Class<?> entityClass);
+
+	boolean exists(Query query, Class<?> entityClass, String collectionName);
+
 	/**
 	 * Map the results of an ad-hoc query on the collection for the entity class to a List of the specified type.
 	 * <p/>

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

@@ -481,6 +481,24 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware {
 		}
 	}
 
+	public boolean exists(Query query, Class<?> entityClass) {
+		return exists(query, entityClass, determineCollectionName(entityClass));
+	}
+
+	public boolean exists(Query query, String collectionName) {
+		return exists(query, null, collectionName);
+	}
+
+	public boolean exists(Query query, Class<?> entityClass, String collectionName) {
+
+		if (query == null) {
+			throw new InvalidDataAccessApiUsageException("Query passed in to exist can't be null");
+		}
+
+		DBObject mappedQuery = mapper.getMappedObject(query.getQueryObject(), getPersistentEntity(entityClass));
+		return execute(collectionName, new FindCallback(mappedQuery)).hasNext();
+	}
+
 	// Find methods that take a Query to express the query and that return a List of objects.
 
 	public <T> List<T> find(Query query, Class<T> entityClass) {

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/repository/support/SimpleMongoRepository.java

@@ -49,13 +49,14 @@ public class SimpleMongoRepository<T, ID extends Serializable> implements MongoR
 	/**
 	 * Creates a ew {@link SimpleMongoRepository} for the given {@link MongoEntityInformation} and {@link MongoTemplate}.
 	 * 
-	 * @param metadata
-	 * @param template
+	 * @param metadata must not be {@literal null}.
+	 * @param template must not be {@literal null}.
 	 */
 	public SimpleMongoRepository(MongoEntityInformation<T, ID> metadata, MongoOperations mongoOperations) {
 
 		Assert.notNull(mongoOperations);
 		Assert.notNull(metadata);
+
 		this.entityInformation = metadata;
 		this.mongoOperations = mongoOperations;
 	}
@@ -114,11 +115,8 @@ public class SimpleMongoRepository<T, ID extends Serializable> implements MongoR
 	public boolean exists(ID id) {
 
 		Assert.notNull(id, "The given id must not be null!");
-
-		final Query idQuery = getIdQuery(id);
-		idQuery.fields();
-
-		return mongoOperations.findOne(idQuery, entityInformation.getJavaType(), entityInformation.getCollectionName()) != null;
+		return mongoOperations.exists(getIdQuery(id), entityInformation.getJavaType(),
+				entityInformation.getCollectionName());
 	}
 
 	/*
@@ -126,7 +124,6 @@ public class SimpleMongoRepository<T, ID extends Serializable> implements MongoR
 	 * @see org.springframework.data.repository.CrudRepository#count()
 	 */
 	public long count() {
-
 		return mongoOperations.getCollection(entityInformation.getCollectionName()).count();
 	}
 
@@ -166,7 +163,6 @@ public class SimpleMongoRepository<T, ID extends Serializable> implements MongoR
 	 * @see org.springframework.data.repository.CrudRepository#deleteAll()
 	 */
 	public void deleteAll() {
-
 		mongoOperations.remove(new Query(), entityInformation.getCollectionName());
 	}
 
@@ -227,7 +223,6 @@ public class SimpleMongoRepository<T, ID extends Serializable> implements MongoR
 	 * @return
 	 */
 	protected MongoOperations getMongoOperations() {
-
 		return this.mongoOperations;
 	}
 
@@ -235,7 +230,6 @@ public class SimpleMongoRepository<T, ID extends Serializable> implements MongoR
 	 * @return the entityInformation
 	 */
 	protected MongoEntityInformation<T, ID> getEntityInformation() {
-
 		return entityInformation;
 	}
 }

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

@@ -1612,6 +1612,19 @@ public class MongoTemplateTests {
 		assertThat(result.get(0).containsField("first"), is(true));
 	}
 
+	@Test
+	public void executesExistsCorrectly() {
+
+		Sample sample = new Sample();
+		template.save(sample);
+
+		Query query = query(where("id").is(sample.id));
+
+		assertThat(template.exists(query, Sample.class), is(true));
+		assertThat(template.exists(query(where("_id").is(sample.id)), template.getCollectionName(Sample.class)), is(true));
+		assertThat(template.exists(query, Sample.class, template.getCollectionName(Sample.class)), is(true));
+	}
+
 	static class MyId {
 
 		String first;