Core Data Migration error when migrating between non-consecutive versions

问题

The Problem

I've got 13 versions of my core data model.
I've made 13 mapping models (V1-V2, V2-V3 etc)
I've got automatic migration switched on.
On migration between two consecutive versions (e.g. V12-V13) the migration works perfectly
On migration between two non-consecutive versions (e.g. V11-V13) the migration fails with the error:

Can't find mapping model for migration

What I've tried

Creating a mapping model for every possible combination of versions. This works, but it's a real hassle.

For version 14 I'll need to make 14 different mapping models. Manually. Ugh.

Code

Here's the options I pass in for migration:

[persistentStoreCoordinator addPersistentStoreWithType:[self storeType]
                                          configuration:nil 
                                                    URL:url 
                                                options:[NSDictionary dictionaryWithObjectsAndKeys:
                                                         [NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption,
                                                         [NSNumber numberWithBool:NO], NSReadOnlyPersistentStoreOption,
                                                         nil]
                                                  error:&error]){

Data Model

My data model is pretty complex, but here it is: http://dl.dropbox.com/u/136780/Engine_V2_DataModel.xcdatamodeld.zip

I'm not using any version hash modifiers or renaming identifiers in my data model right now.

回答1:

See this Stack Overflow question: Core Data Migration Across Multiple Version Upgrades

Basically, the gist is that you don't need to create the complete set of mapping models. You just need mapping models between each pair of successive models, and then you can progressively migrate any old model through the intermediate models to the newest model.

The performance may not be good depending on your store, because you're not doing the migration in one single step. It may be good enough, though, and may be worth it to not have to create the complete set of mapping models. You can also test out the performance of this method to determine whether you need to create maps between non-successive versions of your model.

Marcus Zarra (Core Data aficionado extraordinaire) has the code here: http://media.pragprog.com/titles/mzcd/code/ProgressiveMigration/AppDelegate.m

(I was just about to ask this question, but thanks to LazyTwitter I was pointed to this answer by Aaron Tuller: https://twitter.com/tullera/status/57708304683642880 )

来源：https://stackoverflow.com/questions/5594241/core-data-migration-error-when-migrating-between-non-consecutive-versions

标签

cocoa

core-data

core-data-migration