Do you really need the entire range of an NSUInteger? On iOS that’s an unsigned 32 bit value, which can get very large. It will find into a signed 64 bit. But you probably don’t need that much precision anyway. The maximum for a uint32_t is UINT32_MAX which is 4,294,967,295 (4 billion). If you increment … Read more
Your options are: Use -[NSManagedObject objectID]. Note that this ID is temporary until either the object is saved for the first time or you call -[NSManagedObjectContext obtainPermanentIDsForObjects:error:] Use the CFUUID family of functions to generate a UUID for each object in your -awakeFromInsert method Create your own primary key-like system that stores an integer in … Read more
You should really take a look at RestKit (http://restkit.org) for this use case. It is designed to solve the problems of modeling and syncing remote JSON resources to a local Core Data backed cache. It supports an offline mode for working entirely from the cache when there is no network available. All syncing occurs on … Read more
I’ve figured out what Apple hints in their documentation. It’s actually very easy but a long way to go before it’s obvious. I’ll illustrate the explanation with an example. The initial situation is this: Data Model Version 1 It’s the model you get when you create a project with the “navigation based app with core … Read more
This is one generic method I came up with to handle and display validation errors on the iPhone. But Marcus is right: You’d probably want to tweak the messages to be more user friendly. But this at least gives you a starting point to see what field didn’t validate and why. – (void)displayValidationError:(NSError *)anError { … Read more
NOTE: This answer is very old. See comments for full history. My recommendation has since changed and I no longer recommend using unassociated NSManagedObject instances. My current recommendation is to use temporary child NSManagedObjectContext instances. Original Answer The easiest way to do this is to create your NSManagedObject instances without an associated NSManagedObjectContext. NSEntityDescription *entity … Read more
This is an extremely confusing topic for people approaching Core Data for the first time. I don’t say this lightly, but with experience, I am confident in saying the Apple documentation is somewhat misleading on this matter (it is in fact consistent if you read it very carefully, but they don’t adequately illustrate why merging … Read more
First, pick a JSON library to use, I personally like TouchJSON but several others out there are quite nice as well. The complicated part, although not very hard, is to convert your managed objects into suitable structures for the conversion. I wrote this real quick so it may have an error or two 🙂 The … Read more
I’ve now found out that this is quite simple – once you know where to look. In my AppDelegate I set-up the NSPersistentStoreCoordinator – and you need to add some options to this to tell it to handle auto-migrate: NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys: [NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption, [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil]; NSError *error; _persistentStoreCoordinator = … Read more
I had exactly the same error message as the original post. I was wrestling with this for hours. It was this line in my AppDelegate.m. NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@”[same with name of xcdatamodeld]” withExtension:@”momd”]; For anyone out there searching this error message and finding this thread….try this first. You must make sure that … Read more