Multiple data models with single persistent store coordinator

Question

I inherited an iOS project that uses Core Data. This project has 8 different data models, no need to say that the project is not that big and that I can not see any good reason for splitting the entities over so many data models.

I am trying to use Encrypted Core Data with the current data models and persistent store coordinators and it is not working at all. Every data model is initialized like this:

    NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"First"
                                              withExtension:@"momd"];

    self.model = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
    
    // Coordinator
    //NSPersistentStoreCoordinator *psc = [EncryptedStore makeStore: self.model passcode: @"pass"];
    [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:self.model];

    NSURL *storeURL = [[[AppDelegate appDelegate] applicationDocumentsDirectory] URLByAppendingPathComponent: @"First.sqlite"];
    
    NSError *error = nil;
    [psc addPersistentStoreWithType:NSSQLiteStoreType
                              configuration:nil
                                        URL:storeURL
                                    options:nil
                                      error:&error];
    
    NSManagedObjectContextConcurrencyType ccType = NSMainQueueConcurrencyType;

    self.context = [[NSManagedObjectContext alloc] initWithConcurrencyType:ccType];
    [self.context setPersistentStoreCoordinator:psc];

So every data model has its own managed object model and its own persistent store coordinator with its persistent store and context.

What I see is that Encrypted Core Data (ECD) is only creating the tables in the firstly created persistent store. My suspicion is that ECD only handles the persistent stores added to a single coordinator. Based on that assumption I am wondering if it is possible to create a single coordinator and add several stores to it.

I am not that familiar with Core Data but I can't see how that would be possible since the coordinator is initialized with the managed object model (that points to a specific data model file containing only a set of the total number of entities in the project).

Any ideas? I really would like to avoid merging all the data models into a single one in order to use a single managed object model and coordinator (Actually I would like to do it but I am sure it would break everything and I don't really have to time for that right now).

Please post the ACTUAL code that is being used. Maybe all you did was comment something out, but it's hard to know what the actual code is when what you post is obviously not what is actually running. Also, what do you mean by "What I see is that Encrypted Core Data (ECD) is only creating the tables in the firstly created persistent store?" Also, please state clearly your objective for this questions, as there seems to be a number of questions in there. — Jody Hagins

Tom Harrington Tom Harrington · Accepted Answer · 2015-11-03T18:34:25

You can't use a single persistent store coordinator without merging the models. However, you don't have to edit your data models-- you can merge them at run time. NSManagedObjectModel offers a couple of different ways to merge multiple models into a single unified model. If you load each model independently and merge them in code, you get a single NSManagedObjectModel representing the combined model from each model file. You could then use that combined model with a single persistent store coordinator.

If you're still using multiple model files, you can add each one separately. This raises a complication though-- how will Core Data know which model file to use when you create a new model object instance? You would have to use the assignObject:toPersistentStore: method on NSManagedObjectContext to tell it which one to use. Every time you create a new instance, you do this as well. This means that you need to keep references to the NSPersistentStore instances for each file, and know which to use in every case.

I should add that I have not used encrypted Core Data so I don't know if this will solve your real problem. This approach will allow multiple model files and multiple persistent stores with a single coordinator, though.

Multiple data models with single persistent store coordinator

1 Answers