CoreData predicate for one to many relationship

问题

I have two entity: A and B. Every element of A can have more elements of B (one to many).

Now I have an item of A and I would to take, in this item, one item B (contained in A) that it has B.field = "myParameter".

How can I generate the Predicate for this?

回答1:

You may be looking for that (tested with MagicalRecord):

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(field LIKE %@) AND (isLinkedToAObject == %@)", myFieldParameter, objectA];

With: ClassB has a property isLinkedToAObject to link it to ClassA.

来源：https://stackoverflow.com/questions/25930232/coredata-predicate-for-one-to-many-relationship