我试图进行以下查询：
@NamedQuery(name="Grade.findGradeByClassGroup",
query= "SELECT gr From Grades gr join DeterminateTable d on gr.DeterminateTableId = d.DeterminateTableId join SchoolYears sy on gr.GradeId = sy.GradeId join ClassGroups cg on cg.schoolYear = sy.YearInt where cg.groupId = :classGroup")
我得到了这个例外：
Caused by: Exception [EclipseLink-6069] (Eclipse Persistence Services - 2.6.0.v20141202-3914740): org.eclipse.persistence.exceptions.QueryException
Exception Description: The field [Grades.GradeId] in this expression has an invalid table in this context.
Query: ReadAllQuery(name="Grade.findGradeByClassGroup" referenceClass=Grade jpql="SELECT gr From Grades gr join DeterminateTable d on gr.DeterminateTableId = d.DeterminateTableId join SchoolYears sy on gr.GradeId = sy.GradeId join ClassGroups cg on cg.schoolYear = sy.YearInt where cg.groupId = :classGroup")
at org.eclipse.persistence.exceptions.QueryException.invalidTableForFieldInExpression(QueryException.java:755)
at org.eclipse.persistence.internal.expressions.FieldExpression.validateNode(FieldExpression.java:325)
at org.eclipse.persistence.expressions.Expression.normalize(Expression.java:3291)
at org.eclipse.persistence.internal.expressions.DataExpression.normalize(DataExpression.java:369)
at org.eclipse.persistence.internal.expressions.FieldExpression.normalize(FieldExpression.java:225)
at org.eclipse.persistence.internal.expressions.CompoundExpression.normalize(CompoundExpression.java:224)
at org.eclipse.persistence.internal.expressions.RelationExpression.normalize(RelationExpression.java:574)
at org.eclipse.persistence.internal.expressions.RelationExpression.normalize(RelationExpression.java:865)
at org.eclipse.persistence.expressions.ExpressionBuilder.normalize(ExpressionBuilder.java:267)
at org.eclipse.persistence.internal.expressions.DataExpression.normalize(DataExpression.java:363)
at org.eclipse.persistence.internal.expressions.FieldExpression.normalize(FieldExpression.java:225)
at org.eclipse.persistence.internal.expressions.CompoundExpression.normalize(CompoundExpression.java:232)
at org.eclipse.persistence.internal.expressions.RelationExpression.normalize(RelationExpression.java:574)
at org.eclipse.persistence.internal.expressions.RelationExpression.normalize(RelationExpression.java:865)
at org.eclipse.persistence.expressions.ExpressionBuilder.normalize(ExpressionBuilder.java:267)
at org.eclipse.persistence.internal.expressions.DataExpression.normalize(DataExpression.java:363)
at org.eclipse.persistence.internal.expressions.QueryKeyExpression.normalize(QueryKeyExpression.java:758)
at org.eclipse.persistence.internal.expressions.QueryKeyExpression.normalize(QueryKeyExpression.java:671)
at org.eclipse.persistence.internal.expressions.CompoundExpression.normalize(CompoundExpression.java:224)
at org.eclipse.persistence.internal.expressions.RelationExpression.normalize(RelationExpression.java:574)
at org.eclipse.persistence.internal.expressions.SQLSelectStatement.normalize(SQLSelectStatement.java:1474)
at org.eclipse.persistence.internal.queries.ExpressionQueryMechanism.buildNormalSelectStatement(ExpressionQueryMechanism.java:550)
at org.eclipse.persistence.internal.queries.ExpressionQueryMechanism.prepareSelectAllRows(ExpressionQueryMechanism.java:1722)
at org.eclipse.persistence.queries.ReadAllQuery.prepareSelectAllRows(ReadAllQuery.java:867)
at org.eclipse.persistence.queries.ReadAllQuery.prepare(ReadAllQuery.java:798)
at org.eclipse.persistence.queries.DatabaseQuery.checkPrepare(DatabaseQuery.java:666)
at org.eclipse.persistence.queries.ObjectLevelReadQuery.checkPrepare(ObjectLevelReadQuery.java:909)
at org.eclipse.persistence.queries.DatabaseQuery.checkPrepare(DatabaseQuery.java:615)
at org.eclipse.persistence.internal.jpa.QueryImpl.getDatabaseQueryInternal(QueryImpl.java:342)
... 65 more
我无法弄清楚什么是错的，试图谷歌但无法得到任何答案......
导致这种情况的原因是什么？