Core data join table, has many through, fetched properties predicate

Question

How do you write a Fetched Property for the Place Entity that will present an Array of Users?

Answer 1

I hope I did understand you correctly. You want a list of users that have checked in at a certain place?

Then you do it the other way around. You fetch all Users that have at least one Checkin with a certain Place.

In Core-Data terms you'll need a subquery for this.

NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"User"];
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SUBQUERY(checkins, $CHECKIN, $CHECKIN.event == %@).@count > 0", place];
request.predicate = predicate;
/* and so on */

There is not much documentation about SUBQUERY. A little bit is written in the discussion of expressionForSubquery:usingIteratorVariable:predicate:.

And the fetched property would be in the Place entity with a destination entity User and the predicate SUBQUERY(checkins, $CHECKIN, $CHECKIN.event == $FETCH_SOURCE).@count > 0