Core Data : What will happen if the previous version of 'xcdatamodel' is missed?

Question

We're developing an app using Core Data.

First, the app had a file named MyApp_001.xcdatamodel , and users have installed it.

Then, we create two branches based on MyApp_001 : MyApp_002 & MyApp_003 .

Now, MyApp_002 has two model version : MyApp_001.xcdatamodel & MyApp_002.xcdatamodel , and the current version is MyApp_002.xcdatamodel , which has some modification on MyApp_001.xcdatamodel .

MyApp_003 has two model version : MyApp_001.xcdatamodel & MyApp_003.xcdatamodel , and the current version is MyApp_003.xcdatamodel , which also has some modification on MyApp_001.xcdatamodel .

What confuses me is : some users have installed MyApp_002 first,
Consider that MyApp_003 doesn't contain the model file MyApp_002.xcdatamodel , when they upgrade the app to MyApp_003 , there might be some problem?

How Core Data migrates the data indeed?

Thanks!

Answer 1

To migrate data to a new model, the old model must be present.

When migrating a data store from one model to a new model, Core Data needs to be able to open the data store. That means you need the model that the store uses-- either the one that created it or, if you've previously migrated to a new model, the model used in the most recent migration. If that model is not present, migration is impossible.

In your case, if users installing version 3 might be upgrading from version 2, then the version 2 model must be present. It's the only way to open a data store that was created with that model.

It doesn't matter that a newer model is based on a specific older model. The fact that version 2 and version 3 are both based on version 1 is completely irrelevant. All that matters for migration is the difference between the current model and the one the data store uses.