CODEWITHSUNDEEP
objective-cioscore-datanspredicaterelationship
holographix
holographix

Reputation: 2557

Core Data NSPredicate for toMany Relationsihp

I've got a problem in the formulation of my query; this is the scenario:

my DB schema

based on this db schema, I know the naming part sucks a little, but this is a project which has been already kicked off, so I've to stick with that.

Now, my goal is to select all the characters with a determined pack_id and a certain category_id, i.e. all the characters from pack 1 in category 5, so this's my NSPredicate

    NSFetchRequest *request = [[NSFetchRequest alloc] init];
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(category_id == %@) AND (charRelationship.pack_id == %@)", [[cat valueForKey:@"category_id"] stringValue], curPack];
    [request setEntity:[NSEntityDescription entityForName:@"Category" inManagedObjectContext:self.managedObjectContext]];
    [request setPredicate:predicate];

    NSError *error;
    NSArray *result = [self.managedObjectContext executeFetchRequest:request error:&error];

as soon as the compiler tries to execute the fetchRequest, it crashes and goes SIGABRT. I really hate the fact that xcode is not even giving me a clue about the exception so that I could figure it out myself. So after blindly trying to fix it with no success, I wonder if there's anybody out there who could help me. I've already red a ton of other threads on SO and elsewhere, but I couldn't find any solution.

thanks a lot

-k-

Upvotes: 0

Views: 258

Answers (2)

GeT
GeT

Reputation: 550

Actually you must not store any id separately for an entity that is associated. E.g.: in your case you could just refer to category from the characters entity like:

[NSPredicate predicateWithFormat:@"catRel = %@", cat];

However, I'm not sure what are you going to do with the snippet. Am I right that you have a Category entity stored in your 'cat' variable, and just going to select it from the database with the predicate? I would say, that a category_id already identifies your category... whatever, try not user "charRelationship.pasck_id == %@" but load the corresponding Character entity and use "charRelationship = %@" where you just put your entity.

Upvotes: 0

ggfela
ggfela

Reputation: 1152

try using ANY for the relationship:

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(category_id == %@) AND (ANY charRelationship.pack_id like %@)", [[cat valueForKey:@"category_id"] stringValue], curPack];

Upvotes: 1

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