core-data – Page 7 – Tarik Billa

CoreData: error: Failed to call designated initializer on NSManagedObject class

August 11, 2023 by Tarik

I think the problem is that Challenges is a NSManagedObject class and you need the designated initializer: initWithEntity:insertIntoManagedObjectContext: instead of Challenges *newChallenge = [[Challenges alloc] init]; Read More..

Core Data -existingObjectWithID:error: causes error 133000

August 9, 2023 by Tarik

The problem is that NSManagedObjectID you pass is temporary. You can check it by calling NSManagedObjectID‘s isTemporaryID method. From docs: Returns a Boolean value that indicates whether the receiver is temporary. Most object IDs return NO. New objects inserted into a managed object context are assigned a temporary ID which is replaced with a permanent … Read more

NSFetchedResultsController: changing predicate not working?

August 8, 2023 by Tarik

I had almost exactly this problem, until I found the hint in a very recent blog post at iphone incubator NSFetchedResultsController is caching the first results. (You probably have something set at initWithFetchRequest:managedObjectContext:sectionNameKeyPath:cacheName) I’m guessing your code (like mine) is a derivation of the CoreData sample, so assuming it’s @”Root”, before you change the predicate, … Read more

Core Data – can’t set empty string as default value for attribute

August 7, 2023 by Tarik

This is a very interesting question. After some testing I don’t think this is possible because of the way the text field in the data model is configured. In principle, you could use the unicode empty-set character of \u2205 to represent a default empty string but the text field does not seem to accept any … Read more

How to fetch only the first record in Core Data?

August 5, 2023 by Tarik

You can use the setFetchLimit: method on NSFetchRequest to limit the number of records fetched. So if you only want the first record: // Given some existing NSFetchRequest *request and NSManagedObjectContext *context: [request setFetchLimit:1]; NSError *error; NSArray *results = [context executeFetchRequest:request error:&error]; Note that the call to executeFetchRequest:error: will still return an NSArray; you still … Read more

Xcode-beta 8. Can’t create core data

August 4, 2023 by Tarik

There are two bugs in XCode 8 here: 1 – If you change the Codegen dropdown, it’s new value isn’t saved in Model.xcdatamodel. You have to change something else to get it to save. For example change the class name; build; change the class name back; build again. 2 – The generated code is placed … Read more

Core Data – How to fetch an entity with max value property

August 4, 2023 by Tarik

You set the fetchLimit to 1 and sort by personId in descending order. E.g.: NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@”Person”]; fetchRequest.fetchLimit = 1; fetchRequest.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@”personId” ascending:NO]]; NSError *error = nil; id person = [managedObjectContext executeFetchRequest:fetchRequest error:&error].firstObject;