NonUniqueResultException in findAll() with Spring Data Jpa and Java8 CompletableFuture - asynchronous

Question

I'm trying to make my Jpa repositories asynchronous, see https://github.com/spring-projects/spring-data-examples/tree/master/jpa/java8
Here's my code:
#Configuration
#EnableJpaRepositories(basePackages = "..")
#ComponentScan( {".."} )
#EnableJpaAuditing(..)
#EnableAsync
public class ServicesConfig {
...
}
public interface AsyncRegistrationRepository extends JpaRepository<Registration, Long> {
#Async
#Query("select r from Registration r")
CompletableFuture<List<Registration>> findAllAsync();
}
#Test
#Transactional(propagation = Propagation.NOT_SUPPORTED)
public void testFindAllAsync() throws Exception {
asyncRegistrationRepository.save(randomRegistration(randomToken()));
asyncRegistrationRepository.save(randomRegistration(randomToken()));
asyncRegistrationRepository.save(randomRegistration(randomToken()));
final CompletableFuture<Void> future = asyncRegistrationRepository.findAllAsync().thenAccept(registrations -> {
assertThat(registrations.size()).isEqualTo(3);
registrations.forEach(registration -> LOG.debug(registration.toString()));
LOG.debug("finished");
});
while (!future.isDone()) {
LOG.debug("Waiting for the CompletableFuture to finish...");
TimeUnit.MILLISECONDS.sleep(500);
}
future.get();
}
But when I run my test, throws a NonUniqueResultException, and I don't really know why.. Here's the full stacktrace:
java.util.concurrent.ExecutionException: javax.persistence.NonUniqueResultException: result returns more than one elements
at java.util.concurrent.CompletableFuture.reportGet(CompletableFuture.java:357)
at java.util.concurrent.CompletableFuture.get(CompletableFuture.java:1895)
at net.twentyfourseven.registration.core.repository.AsyncRegistrationRepositoryTest.testFindAllAsync(AsyncRegistrationRepositoryTest.java:86)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:74)
at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:85)
at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:86)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:241)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:87)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:180)
at org.junit.runner.JUnitCore.run(JUnitCore.java:160)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:78)
at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:212)
at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:68)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:140)
Caused by: javax.persistence.NonUniqueResultException: result returns more than one elements
at org.hibernate.jpa.internal.QueryImpl.getSingleResult(QueryImpl.java:492)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at org.springframework.orm.jpa.SharedEntityManagerCreator$DeferredQueryInvocationHandler.invoke(SharedEntityManagerCreator.java:362)
at com.sun.proxy.$Proxy74.getSingleResult(Unknown Source)
at org.springframework.data.jpa.repository.query.JpaQueryExecution$SingleEntityExecution.doExecute(JpaQueryExecution.java:206)
at org.springframework.data.jpa.repository.query.JpaQueryExecution.execute(JpaQueryExecution.java:78)
at org.springframework.data.jpa.repository.query.AbstractJpaQuery.doExecute(AbstractJpaQuery.java:100)
at org.springframework.data.jpa.repository.query.AbstractJpaQuery.execute(AbstractJpaQuery.java:91)
at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.doInvoke(RepositoryFactorySupport.java:413)
at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.invoke(RepositoryFactorySupport.java:391)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
at org.springframework.data.projection.DefaultMethodInvokingMethodInterceptor.invoke(DefaultMethodInvokingMethodInterceptor.java:61)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:98)
at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:262)
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:95)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:136)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
at org.springframework.data.jpa.repository.support.CrudMethodMetadataPostProcessor$CrudMethodMetadataPopulatingMethodIntercceptor.invoke(CrudMethodMetadataPostProcessor.java:122)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:207)
at com.sun.proxy.$Proxy70.findAllAsync(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:302)
at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:190)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157)
at org.springframework.aop.interceptor.AsyncExecutionInterceptor$1.call(AsyncExecutionInterceptor.java:108)
at org.springframework.aop.interceptor.AsyncExecutionAspectSupport$CompletableFutureDelegate$1.get(AsyncExecutionAspectSupport.java:237)
at java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1590)
at java.lang.Thread.run(Thread.java:745)
I have to mention that I'm new to Java8 and maybe the problem is just, that I use the CompletableFuture in a wrong way. But in the link above, the test is working and mine is almost the same.
Thanks in advance for all ideas and suggestions!
P.S.: I'm using hibernate-entitymanager 5.0.0.Final, Spring 4.2.0.RELEASE, spring-data-jpa 1.8.2.RELEASE.