DATAMONGO-1454 - Add support for exists projection in repository query methods.

We now support exists projections for query methods in query methods for derived and string queries.

public PersonRepository extends Repository<Person, String> {

  boolean existsByFirstname(String firstname);

  @ExistsQuery(value = "{ 'lastname' : ?0 }")
  boolean someExistQuery(String lastname);

  @query(value = "{ 'lastname' : ?0 }", exists = true)
  boolean anotherExistQuery(String lastname);
}

Original pull request: #381.

Author: mp911de

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

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2016 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.mongodb.repository;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+import org.springframework.core.annotation.AliasFor;
+
+/**
+ * Annotation to declare finder exists queries directly on repository methods. Both attributes allow using a placeholder
+ * notation of {@code ?0}, {@code ?1} and so on.
+ *
+ * @author Mark Paluch
+ * @since 1.10
+ */
+@Retention(RetentionPolicy.RUNTIME)
+@Target({ ElementType.METHOD, ElementType.ANNOTATION_TYPE })
+@Documented
+@Query(exists = true)
+public @interface ExistsQuery {
+
+	/**
+	 * Takes a MongoDB JSON string to define the actual query to be executed. This one will take precedence over the
+	 * method name then. Alias for {@link Query#value}.
+	 *
+	 * @return
+	 */
+	@AliasFor(annotation = Query.class)
+	String value() default "";
+}

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

@@ -62,6 +62,14 @@
 	 */
 	boolean count() default false;
 
+	/**
+	 * Returns whether the query defined should be executed as exists projection.
+	 *
+	 * @since 1.10
+	 * @return
+	 */
+	boolean exists() default false;
+
 	/**
 	 * Returns whether the query should delete matching documents.
 	 * 

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

@@ -20,7 +20,9 @@
 import org.springframework.data.mongodb.core.MongoOperations;
 import org.springframework.data.mongodb.core.query.Query;
 import org.springframework.data.mongodb.repository.query.MongoQueryExecution.CollectionExecution;
+import org.springframework.data.mongodb.repository.query.MongoQueryExecution.CountExecution;
 import org.springframework.data.mongodb.repository.query.MongoQueryExecution.DeleteExecution;
+import org.springframework.data.mongodb.repository.query.MongoQueryExecution.ExistsExecution;
 import org.springframework.data.mongodb.repository.query.MongoQueryExecution.GeoNearExecution;
 import org.springframework.data.mongodb.repository.query.MongoQueryExecution.PagedExecution;
 import org.springframework.data.mongodb.repository.query.MongoQueryExecution.PagingGeoNearExecution;
@@ -40,6 +42,7 @@
  * @author Oliver Gierke
  * @author Thomas Darimont
  * @author Christoph Strobl
+ * @author Mark Paluch
  */
 public abstract class AbstractMongoQuery implements RepositoryQuery {
 
@@ -123,8 +126,12 @@ private MongoQueryExecution getExecutionToWrap(Query query, MongoParameterAccess
 			return new CollectionExecution(operations, accessor.getPageable());
 		} else if (method.isPageQuery()) {
 			return new PagedExecution(operations, accessor.getPageable());
+		} else if (isCountQuery()) {
+			return new CountExecution(operations);
+		} else if (isExistsQuery()) {
+			return new ExistsExecution(operations);
 		} else {
-			return new SingleEntityExecution(operations, isCountQuery());
+			return new SingleEntityExecution(operations);
 		}
 	}
 
@@ -164,6 +171,14 @@ protected Query createCountQuery(ConvertingParameterAccessor accessor) {
 	 */
 	protected abstract boolean isCountQuery();
 
+	/**
+	 * Returns whether the query should get an exists projection applied.
+	 *
+	 * @return
+	 * @since 1.10
+	 */
+	protected abstract boolean isExistsQuery();
+
 	/**
 	 * Return weather the query should delete matching documents.
 	 * 

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

@@ -164,15 +164,57 @@ public long get() {
 	final class SingleEntityExecution implements MongoQueryExecution {
 
 		private final MongoOperations operations;
-		private final boolean countProjection;
 
 		/*
 		 * (non-Javadoc)
 		 * @see org.springframework.data.mongodb.repository.query.AbstractMongoQuery.Execution#execute(org.springframework.data.mongodb.core.query.Query, java.lang.Class, java.lang.String)
 		 */
 		@Override
 		public Object execute(Query query, Class<?> type, String collection) {
-			return countProjection ? operations.count(query, type, collection) : operations.findOne(query, type, collection);
+			return operations.findOne(query, type, collection);
+		}
+	}
+
+	/**
+	 * {@link MongoQueryExecution} to perform a count projection.
+	 *
+	 * @author Oliver Gierke
+	 * @author Mark Paluch
+	 * @since 1.10
+	 */
+	@RequiredArgsConstructor
+	static final class CountExecution implements MongoQueryExecution {
+
+		private final MongoOperations operations;
+
+		/*
+		 * (non-Javadoc)
+		 * @see org.springframework.data.mongodb.repository.query.AbstractMongoQuery.Execution#execute(org.springframework.data.mongodb.core.query.Query, java.lang.Class, java.lang.String)
+		 */
+		@Override
+		public Object execute(Query query, Class<?> type, String collection) {
+			return operations.count(query, type, collection);
+		}
+	}
+
+	/**
+	 * {@link MongoQueryExecution} to perform an exists projection.
+	 *
+	 * @author Mark Paluch
+	 * @since 1.10
+	 */
+	@RequiredArgsConstructor
+	static final class ExistsExecution implements MongoQueryExecution {
+
+		private final MongoOperations operations;
+
+		/*
+		 * (non-Javadoc)
+		 * @see org.springframework.data.mongodb.repository.query.AbstractMongoQuery.Execution#execute(org.springframework.data.mongodb.core.query.Query, java.lang.Class, java.lang.String)
+		 */
+		@Override
+		public Object execute(Query query, Class<?> type, String collection) {
+			return operations.exists(query, type, collection);
 		}
 	}
 

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

@@ -42,6 +42,7 @@
  * @author Oliver Gierke
  * @author Christoph Strobl
  * @author Thomas Darimont
+ * @author Mark Paluch
  */
 public class PartTreeMongoQuery extends AbstractMongoQuery {
 
@@ -143,6 +144,15 @@ protected boolean isCountQuery() {
 		return tree.isCountProjection();
 	}
 
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.mongodb.repository.query.AbstractMongoQuery#isExistsQuery()
+	 */
+	@Override
+	protected boolean isExistsQuery() {
+		return tree.isExistsProjection();
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.data.mongodb.repository.query.AbstractMongoQuery#isDeleteQuery()

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

@@ -43,16 +43,18 @@
  * @author Oliver Gierke
  * @author Christoph Strobl
  * @author Thomas Darimont
+ * @author Mark Paluch
  */
 public class StringBasedMongoQuery extends AbstractMongoQuery {
 
-	private static final String COUND_AND_DELETE = "Manually defined query for %s cannot be both a count and delete query at the same time!";
+	private static final String COUNT_EXISTS_AND_DELETE = "Manually defined query for %s cannot be a count and exists or delete query at the same time!";
 	private static final Logger LOG = LoggerFactory.getLogger(StringBasedMongoQuery.class);
 	private static final ParameterBindingParser BINDING_PARSER = ParameterBindingParser.INSTANCE;
 
 	private final String query;
 	private final String fieldSpec;
 	private final boolean isCountQuery;
+	private final boolean isExistsQuery;
 	private final boolean isDeleteQuery;
 	private final List<ParameterBinding> queryParameterBindings;
 	private final List<ParameterBinding> fieldSpecParameterBindings;
@@ -96,14 +98,26 @@ public StringBasedMongoQuery(String query, MongoQueryMethod method, MongoOperati
 		this.fieldSpec = BINDING_PARSER.parseAndCollectParameterBindingsFromQueryIntoBindings(
 				method.getFieldSpecification(), this.fieldSpecParameterBindings);
 
-		this.isCountQuery = method.hasAnnotatedQuery() ? method.getQueryAnnotation().count() : false;
-		this.isDeleteQuery = method.hasAnnotatedQuery() ? method.getQueryAnnotation().delete() : false;
+		this.parameterBinder = new ExpressionEvaluatingParameterBinder(expressionParser, evaluationContextProvider);
 
-		if (isCountQuery && isDeleteQuery) {
-			throw new IllegalArgumentException(String.format(COUND_AND_DELETE, method));
-		}
+		if (method.hasAnnotatedQuery()) {
 
-		this.parameterBinder = new ExpressionEvaluatingParameterBinder(expressionParser, evaluationContextProvider);
+			org.springframework.data.mongodb.repository.Query queryAnnotation = method.getQueryAnnotation();
+
+			this.isCountQuery = queryAnnotation.count();
+			this.isExistsQuery = queryAnnotation.exists();
+			this.isDeleteQuery = queryAnnotation.delete();
+
+			if (hasAmbiguousProjectionFlags(this.isCountQuery, this.isExistsQuery, this.isDeleteQuery)) {
+				throw new IllegalArgumentException(String.format(COUNT_EXISTS_AND_DELETE, method));
+			}
+
+		} else {
+
+			this.isCountQuery = false;
+			this.isExistsQuery = false;
+			this.isDeleteQuery = false;
+		}
 	}
 
 	/*
@@ -136,6 +150,15 @@ protected boolean isCountQuery() {
 		return isCountQuery;
 	}
 
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.mongodb.repository.query.AbstractMongoQuery#isExistsQuery()
+	 */
+	@Override
+	protected boolean isExistsQuery() {
+		return isExistsQuery;
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.data.mongodb.repository.query.AbstractMongoQuery#isDeleteQuery()
@@ -145,12 +168,30 @@ protected boolean isDeleteQuery() {
 		return this.isDeleteQuery;
 	}
 
+	private static boolean hasAmbiguousProjectionFlags(boolean isCountQuery, boolean isExistsQuery, boolean isDeleteQuery) {
+		return countBooleanValues(isCountQuery, isExistsQuery, isDeleteQuery) > 1;
+	}
+
+	private static int countBooleanValues(boolean... values) {
+
+		int count = 0;
+
+		for (boolean value : values) {
+
+			if (value) {
+				count++;
+			}
+		}
+
+		return count;
+	}
+
 	/**
 	 * A parser that extracts the parameter bindings from a given query string.
 	 *
 	 * @author Thomas Darimont
 	 */
-	static enum ParameterBindingParser {
+	enum ParameterBindingParser {
 
 		INSTANCE;
 
@@ -257,7 +298,7 @@ private static void collectParameterReferencesIntoBindings(List<ParameterBinding
 
 			} else if (value instanceof Pattern) {
 
-				String string = ((Pattern) value).toString().trim();
+				String string = value.toString().trim();
 				Matcher valueMatcher = PARSEABLE_BINDING_PATTERN.matcher(string);
 
 				while (valueMatcher.find()) {

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

@@ -588,6 +588,23 @@ public void executesAnnotatedCountProjection() {
 		assertThat(repository.someCountQuery("Matthews"), is(2L));
 	}
 
+	/**
+	 * @see DATAMONGO-1454
+	 */
+	@Test
+	public void executesDerivedExistsProjectionToBoolean() {
+		assertThat(repository.existsByFirstname("Oliver August"), is(true));
+		assertThat(repository.existsByFirstname("Hans Peter"), is(false));
+	}
+
+	/**
+	 * @see DATAMONGO-1454
+	 */
+	@Test
+	public void executesAnnotatedExistProjection() {
+		assertThat(repository.someExistQuery("Matthews"), is(true));
+	}
+
 	/**
 	 * @see DATAMONGO-701
 	 */

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

@@ -43,6 +43,7 @@
  * @author Thomas Darimont
  * @author Christoph Strobl
  * @author Fırat KÜÇÜK
+ * @author Mark Paluch
  */
 public interface PersonRepository extends MongoRepository<Person, String>, QueryDslPredicateExecutor<Person> {
 
@@ -251,6 +252,17 @@ public interface PersonRepository extends MongoRepository<Person, String>, Query
 	@Query(value = "{ 'lastname' : ?0 }", count = true)
 	long someCountQuery(String lastname);
 
+	/**
+	 * @see DATAMONGO-1454
+	 */
+	boolean existsByFirstname(String firstname);
+
+	/**
+	 * @see DATAMONGO-1454
+	 */
+	@ExistsQuery(value = "{ 'lastname' : ?0 }")
+	boolean someExistQuery(String lastname);
+
 	/**
 	 * @see DATAMONGO-770
 	 */

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

@@ -313,6 +313,7 @@ private MongoQueryFake createQueryForMethod(String methodName, Class<?>... param
 	private static class MongoQueryFake extends AbstractMongoQuery {
 
 		private boolean isCountQuery;
+		private boolean isExistsQuery;
 		private boolean isDeleteQuery;
 
 		public MongoQueryFake(MongoQueryMethod method, MongoOperations operations) {
@@ -329,6 +330,11 @@ protected boolean isCountQuery() {
 			return isCountQuery;
 		}
 
+		@Override
+		protected boolean isExistsQuery() {
+			return false;
+		}
+
 		@Override
 		protected boolean isDeleteQuery() {
 			return isDeleteQuery;