Core Data: Using Predicates with to-many Relationship - core-data

Question

To-Many relationship in Entity "Meetings" <--->> "Users"
I made a NSManagedSubclass for "Meetings" and it has a property:
#property (nonatomic, retain) NSSet *users;
Objects in *users save fine and I can see them. But when I try to fetch, nothing happens. I have the breakpoint setup inside the Block and it seems like the fetch Block never reaches the breakpoint. No errors. Applications is still running.
I have the following code:
NSString *userName = #"iphone";
NSLog(#"Username %#", userName);
NSFetchRequest *request = [[NSFetchRequest alloc] initWithEntityName:#"Meeting"];
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"users.username == %#", userName];
NSLog(#"Predicate %#", predicate);
[request setPredicate:predicate];
[self.managedObjectContext executeFetchRequest:request onSuccess:^(NSArray *results)
{ // I have setup the breakpoint here
NSLog(#"results.count %i", results.count);
if(results.count > 0)
{
NSLog(#"object found");
}
}onFailure:^(NSError *error) {
NSLog(#"There was an error! %#", error);
}];
Log:
2013-10-12 20:10:19.200 App[3128:c07] Username iphone
2013-10-12 20:10:19.200 App[3128:c07] Predicate users.username == "iphone"
I can fetch for other attributes in Meetings just fine. i.e. If I replace the predicate line with :
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"meetings_id == %#", meetings_id];
And the breakpoint will stop the code, the will show "object found".
Again, I can see the "iphone" user inside the users relationship. What am I doing wrong?

Answer 1

For to-many relationships you have to use a predicate modifier, that states what is the intended behaviour. Since you are searching for Meetings, CoreData cannot figure out from your predicate users.username == %#, if you want Meetings where ALL users have the specified username or only those where ANY single user meets the requirements (see here for in-depth documentation).
Try this for a change, since I think it is what you would want:
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"ANY users.username == %#", userName]