Correctly handle exists when it should return false.

In the previous implementation it would throw an exception.

Original pull request #2368

Author: schauder

src/main/java/org/springframework/data/jpa/repository/support/SimpleJpaRepository.java

@@ -75,8 +75,8 @@
  * @author Moritz Becker
  * @author Sander Krabbenborg
  * @author Jesse Wouters
- * @param <T> the type of the entity to handle
- * @param <ID> the type of the entity's identifier
+ * @author Greg Turnquist
+ * @author Yanming Zhou
  */
 @Repository
 @Transactional(readOnly = true)
@@ -527,12 +527,13 @@ public <S extends T> long count(Example<S> example) {
 	 */
 	@Override
 	public <S extends T> boolean exists(Example<S> example) {
+
 		Specification<S> spec = new ExampleSpecification<>(example, this.escapeCharacter);
 		CriteriaQuery<Integer> cq = this.em.getCriteriaBuilder().createQuery(Integer.class);
 		cq.select(this.em.getCriteriaBuilder().literal(1));
 		applySpecificationToCriteria(spec, example.getProbeType(), cq);
 		TypedQuery<Integer> query = applyRepositoryMethodMetadata(this.em.createQuery(cq));
-		return query.setMaxResults(1).getSingleResult() != null;
+		return query.setMaxResults(1).getResultList().size() == 1;
 	}
 
 	/*

src/test/java/org/springframework/data/jpa/repository/UserRepositoryTests.java

@@ -2058,6 +2058,20 @@ void existsByExampleWithExcludedAttributes() {
 		assertThat(exists).isEqualTo(true);
 	}
 
+	@Test // GH-2368
+	void existsByExampleNegative() {
+
+		flushTestUsers();
+
+		User prototype = new User();
+		prototype.setAge(4711); // there is none with that age
+
+		Example<User> example = Example.of(prototype, matching().withIgnorePaths("createdAt"));
+		boolean exists = repository.exists(example);
+
+		assertThat(exists).isEqualTo(false);
+	}
+
 	@Test // DATAJPA-905
 	void executesPagedSpecificationSettingAnOrder() {