Core Data predicate : unimplemented SQL generation for predicate - ios

Question

Basically I got 3 entities in my data model : Brand, Model and Trim.
A brand has a one-to-many relationship with Model called "models". (one brand have multiple models but a model has only one brand)
A model has a many-to-many relationship with Trim called "trims". (a model can have multiple trims, and a trim can have multiple models)
Having an array of trims objects, I would like to get all the brands having a model which "contains" at least one trim contained inside this array.
So here is my predicate for the fetch request :
NSFetchRequest *request = [[NSFetchRequest alloc] initWithEntityName:#"Brand"];
[NSPredicate predicateWithFormat:#"ANY models.trims IN %#", arrayOfTrims];
And here is the error I'm getting :
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'unimplemented SQL generation for predicate : (ANY models.trims IN {<Trim: 0x8e60340> (entity: Trim; id: 0x8e62f10 <x-coredata://BCD28560-AED5-4409-9A35-1925001773E6/Trim/p8>
I'm kinda new to Core Data and I have no idea what I'm doing wrong.
Hope someone can help,
Thanks a lot.

Answer 1

"ANY" in a Core Data predicate works only for a single to-many relationship.
Since your query involves two to-many relationships, you have to use a SUBQUERY:
[NSPredicate predicateWithFormat:#"SUBQUERY(models, $m, ANY $m.trims IN %#).#count > 0",
arrayOfTrims];

Answer 2

This exception is also raised if one of the predicates uses a column (i.e. field) name that does not exist. Totally misleading error message...

Answer 3

When you use a predicate in a CoreData operation, the predicate gets translated into SQL. That translation is not possible for all NSPredicate operations, you've hit one that isn't. My suggestion would be something along the lines of:
NSMutableArray* predicates = [NSMutableArray new];
for(NSString* trim in arrayOfTrims)
{
[predicates addObject:[NSPredicate predicateWithFormat:#"%# IN models.trims", trim]];
}
NSPredicate* predicate = [NSCompoundPredicate orPredicateWithSubpredicates:predicates];

Answer 4

The keyword IN can be used but you cannot apply ANY at the same time as that does not make sense when you turn it into SQL.
The predicate you are most likely looking for is:
[NSPredicate predicateWithFormat:#"models.trims IN %#", arrayOfTrims];
But that isn't going to work in this case either because you are going across a relationship. So what you need to do is reverse the whole thing:
NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:#"Model"];
[request setPredicate:[NSPredicate predicateWithFormat:#"trims in %#", arrayOfTrims]];
NSError *error = nil;
NSArray *modelArray = [moc executeFetchRequest:request error:&error];
if (!modelArray) {
NSLog(#"Error: %#\n%#", [error localizedDescription], [error userInfo]);
}
NSArray parentObjectArray = [modelArray valueForKey:#"${PARENT_RELATIONSHIP_NAME}"];
Basically you are fetching the child objects to satisfy your ANY and then using KVC to retrieve the parent objects that you care about.

Answer 5

In my case I got this error because I made a silly mistake and didn't have the argument in the right data type.
I was trying to do:
let firstPredicate = NSPredicate(format: "firstName BEGINSWITH[cd] %#", firstNameField.stringValue)
and forgot to put the ".stringValue."