Question

Short question:

I want to run a certain code in my app only if my Core Data model has changed (new entities, new properties, etc). How can I determine if the model has changed or not?

Just some pseudo-code:

    if (current_model_version != previous_model_version) {
    //do some code
    } else {
    // do some other code
    }

I’m guessing I might use versionHashes to do this, or isConfiguration:compatibleWithStoreMetadata:, but I’m not certain how.

Some editing for clarity: ‘current’ as in ‘now’ and ‘previous’ as in ‘last time app was launched.’

Answer 1

The answer seems to be isConfiguration:compatibleWithStoreMedia:.

I found some useful information here:

http://mipostel.com/index.php/home/70-core-data-migration-standard-migration-part-2

I set it up this way:

- (BOOL)modelChanged
{
    NSError *error;
    NSURL * sourceURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"db.sqlite"];
    NSDictionary *sourceMetadata = [NSPersistentStoreCoordinator metadataForPersistentStoreOfType:NSSQLiteStoreType URL:sourceURL error:&error];
    BOOL isCompatible = [[self managedObjectModel] isConfiguration:nil compatibleWithStoreMetadata:sourceMetadata];

    return isCompatible;

}

‘self’ is my shared data store, not that it necessarily has to go there.

deanWombourne points out that what this really does is determine whether or not the data can be automatically migrated, so it’s not exactly the solution to the problem I posed. It does serve my needs in this case.