DATAJPA-1044 - JpaCountQueryCreator now uses count distinct for distinct queries.

We now explicitly use a count (distinct x) clause for count queries in case the distinct flag is set on the derived query method.

Updated HibernateQueryUtils to make sure we unwrap the Query proxy properly before we invoke the lookup method via reflection.

Original pull request: #187.

src/main/java/org/springframework/data/jpa/provider/HibernateUtils.java

@@ -63,7 +63,7 @@ public abstract class HibernateUtils {
 			queryInterface = ClassUtils.forName("org.hibernate.query.Query", classLoader);
 		} catch (Exception o_O) {}
 
-		HIBERNATE_QUERY_INTERFACE = queryInterface;
+		HIBERNATE_QUERY_INTERFACE = queryInterface == null ? type : queryInterface;
 		QUERY_STRING_METHOD = HIBERNATE_QUERY_INTERFACE == null ? null
 				: ReflectionUtils.findMethod(HIBERNATE_QUERY_INTERFACE, "getQueryString");
 	}
@@ -76,10 +76,15 @@ public abstract class HibernateUtils {
 	 */
 	public static String getHibernateQuery(Object query) {
 
-		if (HIBERNATE_QUERY_INTERFACE != null && HIBERNATE_QUERY_INTERFACE.isInstance(query)) {
+		if (HIBERNATE_QUERY_INTERFACE != null && QUERY_STRING_METHOD != null
+				&& HIBERNATE_QUERY_INTERFACE.isInstance(query)) {
 			return String.class.cast(ReflectionUtils.invokeMethod(QUERY_STRING_METHOD, query));
 		}
 
+		if (HIBERNATE_QUERY_INTERFACE != null && !HIBERNATE_QUERY_INTERFACE.isInstance(query)) {
+			query = ((javax.persistence.Query) query).unwrap(HIBERNATE_QUERY_INTERFACE);
+		}
+
 		return ((Query) ReflectionUtils.invokeMethod(GET_HIBERNATE_QUERY, query)).getQueryString();
 	}
 }

src/main/java/org/springframework/data/jpa/repository/query/JpaCountQueryCreator.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2008-2013 the original author or authors.
+ * Copyright 2008-2017 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.
@@ -29,6 +29,7 @@ import org.springframework.data.repository.query.parser.PartTree;
  * Special {@link JpaQueryCreator} that creates a count projecting query.
  * 
  * @author Oliver Gierke
+ * @author Marc Lefrançois
  */
 public class JpaCountQueryCreator extends JpaQueryCreator {
 
@@ -59,11 +60,16 @@ public class JpaCountQueryCreator extends JpaQueryCreator {
 	 * @see org.springframework.data.jpa.repository.query.JpaQueryCreator#complete(javax.persistence.criteria.Predicate, org.springframework.data.domain.Sort, javax.persistence.criteria.CriteriaQuery, javax.persistence.criteria.CriteriaBuilder, javax.persistence.criteria.Root)
 	 */
 	@Override
-	@SuppressWarnings({ "unchecked", "rawtypes" })
+	@SuppressWarnings("unchecked")
 	protected CriteriaQuery<? extends Object> complete(Predicate predicate, Sort sort,
 			CriteriaQuery<? extends Object> query, CriteriaBuilder builder, Root<?> root) {
 
-		CriteriaQuery<? extends Object> select = query.select((Expression) builder.count(root));
+		CriteriaQuery<? extends Object> select = query.select(getCountQuery(query, builder, root));
 		return predicate == null ? select : select.where(predicate);
 	}
+
+	@SuppressWarnings("rawtypes")
+	private static Expression getCountQuery(CriteriaQuery<?> query, CriteriaBuilder builder, Root<?> root) {
+		return query.isDistinct() ? builder.countDistinct(root) : builder.count(root);
+	}
 }

src/test/java/org/springframework/data/jpa/repository/query/JpaCountQueryCreatorIntegrationTests.java

@@ -0,0 +1,76 @@
+/*
+ * Copyright 2017 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.jpa.repository.query;
+
+import static org.hamcrest.CoreMatchers.*;
+import static org.junit.Assert.*;
+
+import java.lang.reflect.Method;
+import java.util.List;
+
+import javax.persistence.EntityManager;
+import javax.persistence.PersistenceContext;
+import javax.persistence.TypedQuery;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.data.jpa.domain.sample.Role;
+import org.springframework.data.jpa.domain.sample.User;
+import org.springframework.data.jpa.provider.HibernateUtils;
+import org.springframework.data.jpa.provider.PersistenceProvider;
+import org.springframework.data.projection.SpelAwareProxyProjectionFactory;
+import org.springframework.data.repository.Repository;
+import org.springframework.data.repository.core.support.AbstractRepositoryMetadata;
+import org.springframework.data.repository.query.parser.PartTree;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+
+/**
+ * Integration tests for {@link JpaCountQueryCreator}.
+ * 
+ * @author Oliver Gierke
+ */
+@RunWith(SpringJUnit4ClassRunner.class)
+@ContextConfiguration("classpath:infrastructure.xml")
+public class JpaCountQueryCreatorIntegrationTests {
+
+	@PersistenceContext EntityManager entityManager;
+
+	@Test // DATAJPA-1044
+	public void distinctFlagOnCountQueryIssuesCountDistinct() throws Exception {
+
+		Method method = SomeRepository.class.getMethod("findDistinctByRolesIn", List.class);
+
+		PersistenceProvider provider = PersistenceProvider.fromEntityManager(entityManager);
+		JpaQueryMethod queryMethod = new JpaQueryMethod(method,
+				AbstractRepositoryMetadata.getMetadata(SomeRepository.class), new SpelAwareProxyProjectionFactory(), provider);
+
+		PartTree tree = new PartTree("findDistinctByRolesIn", User.class);
+		ParameterMetadataProvider metadataProvider = new ParameterMetadataProvider(entityManager.getCriteriaBuilder(),
+				queryMethod.getParameters(), provider);
+
+		JpaCountQueryCreator creator = new JpaCountQueryCreator(tree, queryMethod.getResultProcessor().getReturnedType(),
+				entityManager.getCriteriaBuilder(), metadataProvider);
+
+		TypedQuery<? extends Object> query = entityManager.createQuery(creator.createQuery());
+
+		assertThat(HibernateUtils.getHibernateQuery(query), startsWith("select distinct count(distinct"));
+	}
+
+	interface SomeRepository extends Repository<User, Long> {
+		void findDistinctByRolesIn(List<Role> roles);
+	}
+}