在一对多关系中获取对象时的谓词问题
我有一个简单的情况，我有两个与多对多关系相关的实体。
两个对象，警报和标签。当我想获取与给定标签关联的所有警报时，我尝试了以下操作：
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"%@ IN tags", theTag];
我得到的是所有警报，而不仅仅是与该标签相关的警报。
然而，尝试另一种方法是可行的：
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF in %@", theTag.alarms];
由于与代码重用有关的复杂原因，我确实需要第一个方法来工作。任何帮助将不胜感激！谢谢！
I have a simple situation where I have two entities related with Many-To-Many relationship.
Two objects, Alarms and Tags. When I want to fetch all the Alarms associated with a given Tag, I tried this:
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"%@ IN tags", theTag];
What I get is all Alarms, not just those related to the Tag.
However, trying this the other way around works:
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF in %@", theTag.alarms];
For complicated reasons having to do with code reuse, I really need the first one to work. Any help would be much appreciated! Thanks!
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如果您有一个
Tag对象，那么您可以通过执行以下操作来获取其所有警报：如果由于某种奇怪的原因您必须使用获取请求来执行此操作（您不应该这样做），您的谓词应该是：
If you have a
Tagobject, then you can get all of its alarms by doing:If for some bizarre reason you have to do this with a fetch request (which you shouldn't), your predicate should be: