Load a previous model version

Question

I am loading a NSManagedObjectModel model with the initWithContentsOfURL: constructor like this:

NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@\"MyDoc         


        

Answer 1

If you just want to load the version of the model that's compatible with a particular existing store try:

NSError *error = nil;
NSDictionary *storeMetadata = [NSPersistentStoreCoordinator metadataForPersistentStoreOfType:NSSQLiteStoreType 
                                                                                         URL:storeURL 
                                                                                       error:&error];
NSManagedObjectModel *oldManagedObjectModel = [NSManagedObjectModel mergedModelFromBundles:[NSArray arrayWithObject:[NSBundle mainBundle]] 
                                                                          forStoreMetadata:storeMetadata];

Note that if you use XCode version identifiers for your data model versions, the persistent store's current version identifiers are accessible through the NSStoreModelVersionIdentifiersKey entry in the store metadata dictionary.

As far as loading a particular arbitrary version is concerned, the mom files are typically located under the momd directory in your app's bundle, so you could enumerate them using NSFileManager. I believe to find one with a particular version identifier you would have to use NSManagedObjectModel's initWithContentsOfURL: initializer and then inspect the versionIdentifiers property, or use the isConfiguration:compatibleWithStoreMetadata: instance method to determine compatibility.