Question

Below is my find-or-create code:

+ (id)checkIfEntity:(NSString *)entityName 
        withIDValue:(NSString *)entityIDValue 
           forIDKey:(NSString *)entityIDKey 
    existsInContext:(NSManagedObjectContext *)context
{

    // Create fetch request
    NSFetchRequest *request = [[NSFetchRequest alloc] init];
    [request setReturnsObjectsAsFaults:NO];

    // Fetch messages data
    NSEntityDescription *description = [NSEntityDescription entityForName:entityName inManagedObjectContext:context];
    [request setEntity:description];

    // Only include objects that exist (i.e. entityIDKey and entityIDValue's must exist)
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"%@=%@", entityIDKey, entityIDValue];
    [request setPredicate:predicate];    

    // Execute request that returns array of dashboardEntrys
    NSArray *array = [context executeFetchRequest:request error:nil];

    if ( [array count] ) {

        NSLog(@"%@ = %@ DOES EXIST", entityIDKey, entityIDValue);
        return [array objectAtIndex:0];
    }

    NSLog(@"%@ = %@ DOES NOT EXIST", entityIDKey, entityIDValue);
    return [NSEntityDescription insertNewObjectForEntityForName:entityName inManagedObjectContext:context];
}

Please ignore the fact that I’m not employing best-practices by having two return statements – I will this before pushing my code to production.

It works by passing an NSManagedObject entity with entityName, and has an NSPredicate that checks if there’s an entityIDKey with value entityIDValue; entityIDKey = entityIDValue. I’ve also tried with using ==.

Regardless which comparison method I use, the if ( [array count] ) method is never hit, so the second NSLog statement always gets output, delineating that an object that I know exists in my Core Data store doesn’t actually exist. Therefore, I end up with many duplicate entries when I go to display the contents of my store.

Is my NSPredicate statement correct?

    `NSPredicate *predicate = [NSPredicate predicateWithFormat:@"%@=%@", entityIDKey, entityIDValue];`

where entityIDKey = @"userID" and entityIDvalue = @"1234567890"

Thanks!

Answer 1

Yup, the problem was definitely the predicate.

The predicate argument should have been:

%K == %@

not

%@ = %@