Migration Issues with UIManagedDocument

Question

I started using CoreData in my application after the Stanford CS193P tutorials regarding using iOS 5 of the new UIManagedDocument class. The approach itself is pretty simple, but I can't figure out how to deal with the modifications to the models that I continue to make. This is how I instantiate the UIManagedDocument object (inside appDelegate, so that every other class can use it):

if (!self.database) { NSURL *url=[[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject]; url = [url URLByAppendingPathComponent:@"AppName"]; UIManagedDocument *doc = [[UIManagedDocument alloc] initWithFileURL:url]; NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys: [NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption, [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil]; doc.persistentStoreOptions = options; self.database=doc; [doc release]; } 

The problem is that every time I change at least a little of my .xcdatamodel, I can’t get all the contents previously saved in the document, as well as create any new instance. This actually throws the following exception:

 *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'This NSPersistentStoreCoordinator has no persistent stores. It cannot perform a save operation.' 

I thought that setting the "options" property of a managed document would solve the problem, but apparently this is not enough. Can anybody help? Could not find other questions that really fit my exact needs.

Answer 1

Before changing your Core Data model, you should “Add Model Version”.

1. Select the source model file. (e.g. YourProject.xcdatamodel)

2. "Editor" → "Add model version ...". Then add a new version of the model (e.g. 2.0)

3. You will receive a new model file. (e.g. YourProject 2.0.xcdatamodel). Change it.

4. Change the current version of the model. Select the top .xcdtatmodel file → View → Utilities → Show File Inspector. Find the "Versioned Core Data Model" tag and select the version you want to change.

It also bothered me for a long time. Hope this way helps you ^^

Answer 2

There is a very simple solution to your problem. Just remove the application from the simulator or device (touch the application icon for a few seconds and touch the cross that appears when the application icons begin to vibrate). Thus, Xcode updates your UIManagedDocument application.

Answer 3

Make sure that you are not mistaken about NSDocumentDirectory as NSDocumentationDirectory.

  NSURL *url = [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject]; 

NSDocumentDirectory is right!