Я использую JPA 2.1, Hibernate 4.3.6.Final и MySQL 5.5.37. Как мне написать JPQL-запрос, который выполняет соединение? Я пытаюсь ниже

    final String jpqlQuery = "SELECT m FROM Message m LEFT JOIN MessageReadDate mr " + 
            " INNER JOIN m.group g " + 
            " LEFT JOIN g.classroom c " + 
            " LEFT JOIN c.ROSTER u WHERE " + 
            " u.USER = :recipient AND " + 
            " u.ENABLED = 1 AND " + 
            " c.ENABLED = 1 AND " + 
            " g.NAME = '' AND " +
            " m.author <> :author";
    Query query = m_entityManager.createQuery(jpqlQuery);

но появляется сообщение об ошибке «Путь к соединению! … Неверный путь: «классная комната».

org.hibernate.hql.internal.ast.ErrorCounter -  Path expected for join!
 Path expected for join!
        at org.hibernate.hql.internal.ast.HqlSqlWalker.createFromJoinElement(HqlSqlWalker.java:379)
        at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.joinElement(HqlSqlBaseWalker.java:3903)
        at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.fromElement(HqlSqlBaseWalker.java:3689)
        at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.fromElementList(HqlSqlBaseWalker.java:3567)
        at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.fromClause(HqlSqlBaseWalker.java:708)
        at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.query(HqlSqlBaseWalker.java:564)
        at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.selectStatement(HqlSqlBaseWalker.java:301)
        at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.statement(HqlSqlBaseWalker.java:249)
        at org.hibernate.hql.internal.ast.QueryTranslatorImpl.analyze(QueryTranslatorImpl.java:278)
        at org.hibernate.hql.internal.ast.QueryTranslatorImpl.doCompile(QueryTranslatorImpl.java:206)
        at org.hibernate.hql.internal.ast.QueryTranslatorImpl.compile(QueryTranslatorImpl.java:158)
        at org.hibernate.engine.query.spi.HQLQueryPlan.<init>(HQLQueryPlan.java:126)
        at org.hibernate.engine.query.spi.HQLQueryPlan.<init>(HQLQueryPlan.java:88)
        at org.hibernate.engine.query.spi.QueryPlanCache.getHQLQueryPlan(QueryPlanCache.java:167)
        at org.hibernate.internal.AbstractSessionImpl.getHQLQueryPlan(AbstractSessionImpl.java:301)
        at org.hibernate.internal.AbstractSessionImpl.createQuery(AbstractSessionImpl.java:236)
        at org.hibernate.internal.SessionImpl.createQuery(SessionImpl.java:1800)
        at org.hibernate.jpa.spi.AbstractEntityManagerImpl.createQuery(AbstractEntityManagerImpl.java:328)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at org.springframework.orm.jpa.SharedEntityManagerCreator$SharedEntityManagerInvocationHandler.invoke(SharedEntityManagerCreator.java:240)
        at com.sun.proxy.$Proxy68.createQuery(Unknown Source)
        at org.mainco.subco.messaging.repo.MessageDaoImpl.getUnreadClassAnnouncements(MessageDaoImpl.java:161)
        at org.mainco.subco.messaging.repo.MessageDaoImpl.getUnreadMessages(MessageDaoImpl.java:140)
        at org.mainco.subco.messaging.repo.MessageDaoIT.testGetUnreadMessages(MessageDaoIT.java:125)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)
        at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
        at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)
        at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
        at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:  74)
        at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:83)
        at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:72)
        at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:231)
        at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:49)
        at org.junit.runners.ParentRunner$3.run(ParentRunner.java:193)
        at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:52)
        at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:191)
        at org.junit.runners.ParentRunner.access$000(ParentRunner.java:42)
        at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:184)
        at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
        at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:71)
        at org.junit.runners.ParentRunner.run(ParentRunner.java:236)
        at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:174)
        at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
        at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
        at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
        at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
        at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
        at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)
    [ERROR]: org.hibernate.hql.internal.ast.ErrorCounter -  Invalid path: 'g.classroom'
    [ERROR]: org.hibernate.hql.internal.ast.ErrorCounter -  Invalid path: 'g.classroom'
     Invalid path: 'g.classroom'
        at org.hibernate.hql.internal.ast.util.LiteralProcessor.lookupConstant(LiteralProcessor.java:129)
        at org.hibernate.hql.internal.ast.tree.DotNode.resolve(DotNode.java:225)
        at org.hibernate.hql.internal.ast.tree.FromReferenceNode.resolve(FromReferenceNode.java:126)
        at org.hibernate.hql.internal.ast.HqlSqlWalker.createFromJoinElement(HqlSqlWalker.java:387)
        at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.joinElement(HqlSqlBaseWalker.java:3903)
        at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.fromElement(HqlSqlBaseWalker.java:3689)
        at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.fromElementList(HqlSqlBaseWalker.java:3567)
        at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.fromClause(HqlSqlBaseWalker.java:708)
        at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.query(HqlSqlBaseWalker.java:564)
        at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.selectStatement(HqlSqlBaseWalker.java:301)
        at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.statement(HqlSqlBaseWalker.java:249)
        at org.hibernate.hql.internal.ast.QueryTranslatorImpl.analyze(QueryTranslatorImpl.java:278)
        at org.hibernate.hql.internal.ast.QueryTranslatorImpl.doCompile(QueryTranslatorImpl.java:206)
        at org.hibernate.hql.internal.ast.QueryTranslatorImpl.compile(QueryTranslatorImpl.java:158)
    …

Моя сущность сообщения выглядит следующим образом ...

@Entity
@Table(name = "msg")
public class Message
{

    @Id
    @NotNull
    @GeneratedValue(generator = "uuid-strategy")
    @Column(name = "ID")
    private String id;

    @Column(name = "MESSAGE", columnDefinition="LONGTEXT")
    private String message;

    @ManyToOne
    @JoinColumn(name = "GROUP_ID", nullable = false, updatable = true)
    private Group group;

И моя групповая сущность выглядит следующим образом ...

@Entity
@Table(name = "msg_group")
public class Group
{
    @Id
    @NotNull
    @GeneratedValue(generator = "uuid-strategy")
    @Column(name = "ID")
    private String id;

    @Column(name = "NAME")
    private String name;

    @ManyToOne
    @JoinColumn(name = "CLASSROOM_ID", nullable = true, updatable = true)
    private Classroom classroom;

Так почему я не могу сослаться на атрибут «класс»?

Спасибо, Дэйв