CODEWITHSUNDEEP
ioscore-datanspredicate
nemesys
nemesys

Reputation: 554

NSPredicate for 2 to-many relationships

I'm having a problem with the syntax of a NSPredicate. I have 3 entities: A, B and C. A has a many-to-many relationship to B. B has a many-to-many relationship to C. I want to fetch all managed objects in A that have at least one relationship with an object in B which, in turn, has a relationship with at least one object in C.

I have tried a few variations of SUBQUERY and ANY but I'm obviously not using the right syntax.

I have tried:

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *ent = [NSEntityDescription entityForName:@"A" inManagedObjectContext:self.managedObjectContext];
fetchRequest.entity = ent;
fetchRequest.predicate = [NSPredicate predicateWithFormat:@"(SUBQUERY(B, $b, $b.c.@count > 0).@count > 0)"];

That resulted in:

2014-06-30 09:07:12.143 My App[86086:60b] * Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Keypath containing KVC aggregate where there shouldn't be one; failed to handle $b.jobs.@count'

Then:

fetchRequest.predicate = [NSPredicate predicateWithFormat:@"ANY b.c.@count > 0"];

resulted in:

2014-06-30 09:10:14.403 My App[86186:60b] * Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Unsupported function expression count:(b.c)'

Also:

fetchRequest.predicate = [NSPredicate predicateWithFormat:@"(SUBQUERY(B, $b, $b.c.@count > 0))"];

resulted in:

2014-06-30 09:17:25.883 My App[86218:60b] * Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Unable to parse the format string "(SUBQUERY(B, $b, $b.c.@count > 0))"'

Finally:

fetchRequest.predicate = [NSPredicate predicateWithFormat:@"(SUBQUERY(B, $b, $b.c).@count > 0)"];

ended with:

2014-06-30 09:18:30.202 My App[86272:60b] * Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Unable to parse the format string "(SUBQUERY(B, $b, $b.c).@count > 0)"'

Anyone has any idea? There must be an easy way to do this fetch...

Upvotes: 4

Views: 730

Answers (1)

Martin R
Martin R

Reputation: 539685

This should work:

[NSPredicate predicateWithFormat:@"SUBQUERY(bs, $b, ANY $b.cs != NULL).@count > 0"]

where "bs" is the to-many relationship from entity A to B, and "cs" is the to-many relationship from B to C.

Upvotes: 2

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