我确实有3个实体，想交叉加入。因为我不需要为此创建新的实体，所以我只想通过使用本机查询获取来映射：
EntityA{
...
String someValue;
}
EntityB{
...
String someValue;
}
EntityC{
...
String someValue;
}
和交叉连接的对象
CrossJoinedFoo{
EntityA entityA;
EntityB entityB;
EntityC entityC;
}
我使用它像：
private static final String _SELECT_CROSS_JOIN_ENTITIES = "SELECT * FROM "
+ "EntityA"
+ ", "
+ "EntityB"
+ ", "
+ "EntityC"
+ " WHERE (1=1) "
+ " AND " + "EntityA.someValue = :someValue"
+ " AND " + "EntityB.someValue = :someValue"
+ " AND " + "EntityC.someValue = :someValue";
Query query = entityManager.createNativeQuery(_SELECT_CROSS_JOIN_ENTITIES);
query.setParameter(":someValue", "foo");
我该如何实现这种行为？
您可以进行HQL查询并使用结果类策略。只要记住要在CrossJoinedFoo中添加一个构造器即可以适当的顺序接受3个实体：
private static final String _SELECT_CROSS_JOIN_ENTITIES =
"SELECT new my.package.CrossJoinedFoo(a,b,c) FROM "
+ "EntityA a"
+ ", "
+ "EntityB b"
+ ", "
+ "EntityC c"
+ " WHERE (1=1) "
+ " AND " + "a.someValue = :someValue"
+ " AND " + "b.someValue = :someValue"
+ " AND " + "c.someValue = :someValue";
Query query = entityManager.createQuery(_SELECT_CROSS_JOIN_ENTITIES);
query.setParameter(":someValue", "foo");
List<CrossJoinedFoo> result = query.list();
只要记住将软件包更改为适当的软件包即可。
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