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core-datanspredicatensfetchrequest

NSPredicate with relationship child entity property

I have this Model situation -

  1. Group entity is in One on One relationship with Event entity called latestEvent.
  2. Event entity has a child entity called 'WeddingEvent' which is one of many child events.
  3. WeddingEvent is the only one who has a property called present
  4. I am trying to filter Group to not be fetched if the latestEvent is of kind 'WeddingEvent'.

Since I can not fetch by className or by entityName I tried :

NSPredicate *LatestEventValidity = [NSPredicate predicateWithFormat:@"latestEvent.present != nil"];

AND

 NSPredicate *LatestEventValidity = [NSPredicate predicateWithBlock:^BOOL(id evaluatedObject, NSDictionary * bindings) {
        OOVGroup *group = evaluatedObject;
        return [group.latestEvent respondsToSelector:@selector(setPresent:)];
    }];

But they al failed.

Any help here ?

Solution

  • The first predicate does not work because not all Event objects respond to the "present" selector. The second predicate does not work because you cannot use block-based (or any Objective-C based) predicates in a Core Data fetch request.

    The only solution is probably to add a (string or integer) "type" attribute to your "Event" entity, so that you can filter with a predicate like "lastEvent.type != 'Wedding'".