Why "NOT IN" does not work in this NSPredicate?
A . b and B . a are inverse to-many relationships. Why does this predicate for A work:
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"NOT SELF IN %@", bObject.a];
while this one does not:
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"NOT %@ IN b", bObject];
I think both predicates should give the same result — the collection of A s that have no relation with bObject via a<-->b . But in fact, the first one gives the correct collection while the second one not.
Update:
Here is a sample project wherein A . b is embodied by Account . filtered_clients and B . a is embodied by Client . filtered_by .
Toggle commenting of line 143 and line 144 in MasterViewController.m to see the difference.
Please help me either find the bug in my code, or confirm it is a Core Data bug so I can report it to Apple. Thanks very much.
Here is another idea: maybe it is trying to "negate" the bObject with the NOT . Thus, try:
@"NOT (%@ IN b)"
From the documentation:
Important You must define many-to-many relationships in both directions—that is, you must specify two relationships, each being the inverse of the other. You can't just define a to-many relationship in one direction and try to use it as a many-to-many. If you do, you will end up with referential integrity problems.
So check this:
I think I found the answer for people coming across this question. Apparently you do need to use SELF for it to work, at least in my case with two to-many relations. This works for me:
NOT (SELF IN %@)