问题描述
我有三个实体:EntityA、EntityB 和 EntityC，它们以多对多的关系相连.
I have three entities: EntityA, EntityB and EntityC connected with to-many relationships.
有关详细信息，请参阅架构:
See schema for details:
替代文字 http://img706.imageshack.us/img706/9974/screenshot20091220at124.png
为了获取依赖于 EntityB.name 的 EntityA 的所有实例，我使用这样的谓词:
For getting all instance of EntityA which depend from EntityB.name I use the predicate like this:
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"ANY EntityB.name like 'SomeName'"];
获取依赖于 EntityC.name 的所有 EntityA 实例的谓词应该是什么?我尝试了像 @"ANY EntityB.entitiesC.name like 'SomeName'" 这样的查询，但得到异常 "multiple to-many keys not allowed here".
What should be predicate for getting all instance of EntityA which depend from EntityC.name?I tried query like @"ANY EntityB.entitiesC.name like 'SomeName'" but get exception "multiple to-many keys not allowed here".
最好的问候，
维克多
推荐答案
我的最终解决方案是使用 SUBQUERY.
My final solution is to use SUBQUERY.
NSPredicate *p = [NSpredicate predicateWithFormat:@"(name like %@) AND (0 != SUBQUERY(entitiesB, $x, (0 != SUBQUERY($x.entitiesC, $y, $y.name like %@).@count)).@count)", nameA, nameC];
很遗憾，我无法在 nsExpression 对象上扩展此查询.
Unfortunately I was unable to expand this query on nsExpression objects.
这篇关于使用多对多深度关系构建 NSPredicate 的更好方法是什么?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！