DATAJPA-1074 - Added support for IsEmpty/IsNotEmpty keywords in query derivation.

We now translate the newly introduced IsEmpty / IsNotEmpty keywords into the corresponding Criteria API artifacts.

Original pull request: #190.

Author: BigMichi1

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

@@ -48,6 +48,7 @@
  * 
  * @author Oliver Gierke
  * @author Mark Paluch
+ * @author Michael Cramer
  */
 public class JpaQueryCreator extends AbstractQueryCreator<CriteriaQuery<? extends Object>, Predicate> {
 
@@ -306,6 +307,13 @@ public Predicate build() {
 				case NEGATING_SIMPLE_PROPERTY:
 					return builder.notEqual(upperIfIgnoreCase(getTypedPath(root, part)),
 							upperIfIgnoreCase(provider.next(part).getExpression()));
+				case IS_EMPTY:
+				case IS_NOT_EMPTY:
+					if (property.getLeafProperty().isCollection()) {
+						Expression<Collection<Object>> emptyExpression = traversePath(root, property);
+						return type.equals(IS_NOT_EMPTY) ? builder.isNotEmpty(emptyExpression)
+								: builder.isEmpty(emptyExpression);
+					}
 				default:
 					throw new IllegalArgumentException("Unsupported keyword " + type);
 			}

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

@@ -57,6 +57,7 @@
  * 
  * @author Oliver Gierke
  * @author Mark Paluch
+ * @author Michael Cramer
  */
 @RunWith(SpringJUnit4ClassRunner.class)
 @ContextConfiguration("classpath:infrastructure.xml")
@@ -136,6 +137,28 @@ public void shouldSelectAliasedIdForExistsProjectionQueries() throws Exception {
 		assertThat(HibernateUtils.getHibernateQuery(getValue(query, PROPERTY)), containsString(".id from User as"));
 	}
 
+	@Test // DATAJPA-1074
+	public void isEmptyCollection() throws Exception {
+
+		JpaQueryMethod queryMethod = getQueryMethod("findByRolesIsEmpty");
+		PartTreeJpaQuery jpaQuery = new PartTreeJpaQuery(queryMethod, entityManager, provider);
+
+		Query query = jpaQuery.createQuery(new Object[] {});
+
+		assertThat(HibernateUtils.getHibernateQuery(getValue(query, PROPERTY)), endsWith("roles is empty"));
+	}
+
+	@Test // DATAJPA-1074
+	public void isNotEmptyCollection() throws Exception {
+
+		JpaQueryMethod queryMethod = getQueryMethod("findByRolesIsNotEmpty");
+		PartTreeJpaQuery jpaQuery = new PartTreeJpaQuery(queryMethod, entityManager, provider);
+
+		Query query = jpaQuery.createQuery(new Object[] {});
+
+		assertThat(HibernateUtils.getHibernateQuery(getValue(query, PROPERTY)), endsWith("roles is not empty"));
+	}
+
 	private void testIgnoreCase(String methodName, Object... values) throws Exception {
 
 		Class<?>[] parameterTypes = new Class[values.length];
@@ -192,5 +215,9 @@ interface UserRepository extends Repository<User, Long> {
 		boolean existsByFirstname(String firstname);
 
 		List<User> findByCreatedAtAfter(@Temporal(TemporalType.TIMESTAMP) @Param("refDate") Date refDate);
+
+		List<User> findByRolesIsEmpty();
+
+		List<User> findByRolesIsNotEmpty();
 	}
 }