Cannot simultaneously fetch multiple bags

[igdianov]

Executing query:

query { Human(id:"1001") { favoriteDroid { name } appearsIn, friends { name friends { name } } } }

produces the following exception with the stack trace:

javax.persistence.PersistenceException: org.hibernate.loader.MultipleBagFetchException: cannot simultaneously fetch multiple bags: [com.introproventures.graphql.jpa.query.example.model.Character.appearsIn, com.introproventures.graphql.jpa.query.example.model.Character.friends, com.introproventures.graphql.jpa.query.example.model.Character.friends]
	at org.hibernate.jpa.spi.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1692) ~[hibernate-entitymanager-5.0.12.Final.jar:5.0.12.Final]
	at org.hibernate.jpa.spi.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1602) ~[hibernate-entitymanager-5.0.12.Final.jar:5.0.12.Final]
	at org.hibernate.jpa.internal.QueryImpl.getSingleResult(QueryImpl.java:560) ~[hibernate-entitymanager-5.0.12.Final.jar:5.0.12.Final]
	at org.hibernate.jpa.criteria.compile.CriteriaQueryTypeQueryAdapter.getSingleResult(CriteriaQueryTypeQueryAdapter.java:54) ~[hibernate-entitymanager-5.0.12.Final.jar:5.0.12.Final]
	at com.introproventures.graphql.jpa.query.schema.impl.GraphQLJpaSimpleDataFetcher.get(GraphQLJpaSimpleDataFetcher.java:46) ~[classes/:na]
	at graphql.execution.ExecutionStrategy.resolveField(ExecutionStrategy.java:99) ~[graphql-java-3.0.0.jar:na]
	at graphql.execution.SimpleExecutionStrategy.execute(SimpleExecutionStrategy.java:19) [graphql-java-3.0.0.jar:na]
	at graphql.execution.Execution.executeOperation(Execution.java:106) [graphql-java-3.0.0.jar:na]
	at graphql.execution.Execution.execute(Execution.java:49) [graphql-java-3.0.0.jar:na]
	at graphql.GraphQL.execute(GraphQL.java:222) [graphql-java-3.0.0.jar:na]
	at graphql.GraphQL.execute(GraphQL.java:187) [graphql-java-3.0.0.jar:na]
	at com.introproventures.graphql.jpa.query.schema.impl.GraphQLJpaExecutor.execute(GraphQLJpaExecutor.java:68) [classes/:na]
	at com.introproventures.graphql.jpa.query.schema.impl.GraphQLJpaExecutor$$FastClassBySpringCGLIB$$3c8ebb24.invoke(<generated>) [classes/:na]
	at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204) [spring-core-4.3.7.RELEASE.jar:4.3.7.RELEASE]
	at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:721) [spring-aop-4.3.7.RELEASE.jar:4.3.7.RELEASE]
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157) [spring-aop-4.3.7.RELEASE.jar:4.3.7.RELEASE]
	at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:99) [spring-tx-4.3.7.RELEASE.jar:4.3.7.RELEASE]
	at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:282) [spring-tx-4.3.7.RELEASE.jar:4.3.7.RELEASE]
	at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96) [spring-tx-4.3.7.RELEASE.jar:4.3.7.RELEASE]
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) [spring-aop-4.3.7.RELEASE.jar:4.3.7.RELEASE]
	at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:656) [spring-aop-4.3.7.RELEASE.jar:4.3.7.RELEASE]
	at com.introproventures.graphql.jpa.query.schema.impl.GraphQLJpaExecutor$$EnhancerBySpringCGLIB$$17062d1.execute(<generated>) [classes/:na]
	at com.introproventures.graphql.jpa.query.web.GraphQLController.postJson(GraphQLController.java:71) [classes/:na]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_40]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_40]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_40]
	at java.lang.reflect.Method.invoke(Method.java:497) ~[na:1.8.0_40]
	at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205) [spring-web-4.3.7.RELEASE.jar:4.3.7.RELEASE]
	at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:133) [spring-web-4.3.7.RELEASE.jar:4.3.7.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:116) [spring-webmvc-4.3.7.RELEASE.jar:4.3.7.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827) [spring-webmvc-4.3.7.RELEASE.jar:4.3.7.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738) [spring-webmvc-4.3.7.RELEASE.jar:4.3.7.RELEASE]
	at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85) [spring-webmvc-4.3.7.RELEASE.jar:4.3.7.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:963) [spring-webmvc-4.3.7.RELEASE.jar:4.3.7.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897) [spring-webmvc-4.3.7.RELEASE.jar:4.3.7.RELEASE]
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970) [spring-webmvc-4.3.7.RELEASE.jar:4.3.7.RELEASE]
	at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:872) [spring-webmvc-4.3.7.RELEASE.jar:4.3.7.RELEASE]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:648) [tomcat-embed-core-8.5.11.jar:8.5.11]
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846) [spring-webmvc-4.3.7.RELEASE.jar:4.3.7.RELEASE]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:729) [tomcat-embed-core-8.5.11.jar:8.5.11]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:230) [tomcat-embed-core-8.5.11.jar:8.5.11]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) [tomcat-embed-core-8.5.11.jar:8.5.11]
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) [tomcat-embed-websocket-8.5.11.jar:8.5.11]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) [tomcat-embed-core-8.5.11.jar:8.5.11]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) [tomcat-embed-core-8.5.11.jar:8.5.11]
	at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) [spring-web-4.3.7.RELEASE.jar:4.3.7.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.3.7.RELEASE.jar:4.3.7.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) [tomcat-embed-core-8.5.11.jar:8.5.11]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) [tomcat-embed-core-8.5.11.jar:8.5.11]
	at org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:105) [spring-web-4.3.7.RELEASE.jar:4.3.7.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.3.7.RELEASE.jar:4.3.7.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) [tomcat-embed-core-8.5.11.jar:8.5.11]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) [tomcat-embed-core-8.5.11.jar:8.5.11]
	at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:81) [spring-web-4.3.7.RELEASE.jar:4.3.7.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.3.7.RELEASE.jar:4.3.7.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) [tomcat-embed-core-8.5.11.jar:8.5.11]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) [tomcat-embed-core-8.5.11.jar:8.5.11]
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197) [spring-web-4.3.7.RELEASE.jar:4.3.7.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.3.7.RELEASE.jar:4.3.7.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) [tomcat-embed-core-8.5.11.jar:8.5.11]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) [tomcat-embed-core-8.5.11.jar:8.5.11]
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198) [tomcat-embed-core-8.5.11.jar:8.5.11]
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-8.5.11.jar:8.5.11]
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:474) [tomcat-embed-core-8.5.11.jar:8.5.11]
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) [tomcat-embed-core-8.5.11.jar:8.5.11]
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79) [tomcat-embed-core-8.5.11.jar:8.5.11]
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) [tomcat-embed-core-8.5.11.jar:8.5.11]
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:349) [tomcat-embed-core-8.5.11.jar:8.5.11]
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:783) [tomcat-embed-core-8.5.11.jar:8.5.11]
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-8.5.11.jar:8.5.11]
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:798) [tomcat-embed-core-8.5.11.jar:8.5.11]
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1434) [tomcat-embed-core-8.5.11.jar:8.5.11]
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-8.5.11.jar:8.5.11]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_40]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_40]
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-8.5.11.jar:8.5.11]
	at java.lang.Thread.run(Thread.java:745) [na:1.8.0_40]
Caused by: org.hibernate.loader.MultipleBagFetchException: cannot simultaneously fetch multiple bags: [com.introproventures.graphql.jpa.query.example.model.Character.appearsIn, com.introproventures.graphql.jpa.query.example.model.Character.friends, com.introproventures.graphql.jpa.query.example.model.Character.friends]
	at org.hibernate.loader.BasicLoader.postInstantiate(BasicLoader.java:75) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
	at org.hibernate.loader.hql.QueryLoader.<init>(QueryLoader.java:106) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
	at org.hibernate.hql.internal.ast.QueryTranslatorImpl.doCompile(QueryTranslatorImpl.java:211) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
	at org.hibernate.hql.internal.ast.QueryTranslatorImpl.compile(QueryTranslatorImpl.java:142) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
	at org.hibernate.engine.query.spi.HQLQueryPlan.<init>(HQLQueryPlan.java:115) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
	at org.hibernate.engine.query.spi.HQLQueryPlan.<init>(HQLQueryPlan.java:81) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
	at org.hibernate.internal.AbstractQueryImpl.applyEntityGraphQueryHint(AbstractQueryImpl.java:1056) ~[hibernate-core-5.0.12.Final.jar:5.0.12.Final]
	at org.hibernate.jpa.internal.QueryImpl.list(QueryImpl.java:604) ~[hibernate-entitymanager-5.0.12.Final.jar:5.0.12.Final]
	at org.hibernate.jpa.internal.QueryImpl.getSingleResult(QueryImpl.java:529) ~[hibernate-entitymanager-5.0.12.Final.jar:5.0.12.Final]
	... 74 common frames omitted

[igdianov]

When we use Collection or List type in @ManyToMany or @OneToMany associations like below

    @GraphQLDescription("Who are the known friends to this character")
    @ManyToMany
    @JoinTable(name="character_friends",
            joinColumns=@JoinColumn(name="source_id", referencedColumnName="id"),
            inverseJoinColumns=@JoinColumn(name="friend_id", referencedColumnName="id"))
    Collection<Character> friends;

Hibernate underneath JPA cannot use java.util.List or java.util.Collection for fetching eagerly associations with more than two levels of nesting for collections while using generated fetch graph to optimize query performance.

One workaround solution is to replace bag semantics with List semantics. This can be done by adding the @IndexColumn on the relation. The usage of @IndexColumn helps solving the problem since now Hibernate has a List semantic for the association and when fetching the parent it also fetches the index of each element on the list. Using this index Hibernate can tell if the element on the list has already been loaded

The other solution is to use java.util.Set instead when defining collection attributes.

    @GraphQLDescription("Who are the known friends to this character")
    @ManyToMany
    @JoinTable(name="character_friends",
            joinColumns=@JoinColumn(name="source_id", referencedColumnName="id"),
            inverseJoinColumns=@JoinColumn(name="friend_id", referencedColumnName="id"))
    Set<Character> friends;