Can't find mapping model for migration - UIManagedDocument Core Data Migration

Question

I have two versions of my model Model001.xcdatamodel and Model002.xcdatamodel. These two are in the Model.xcdatamodeld bundle. I also have

Answer 1

This can happen if your test device's store is from a version of the data model that no longer exists.

For example I had Data Model Version 7, then I made Data Model Version 8. I made a mapping model to go from 7 to 8. Then I ran it on my test device and everything was happy.

Then I made some more changes to 8.

The thing to realize is that in Core Data, every model has a hash identifier that the system creates by taking a checksum of the xcdatamodel file. So if you make even a slight change, even if you didn't create a new version, it sees it as a different version. These versions' identifiers are NSStoreModelVersionHashes (see documentation here).

So in other words, I ended up with:

Data Model 7 (release) - 0plcXXRN7XHKl5CcF+fwriFmUpON3ZtcI/AfK748aWc=

Data Model 8 (beta)    - qeN1Ym3TkWN1G6dU9RfX6Kd2ccEvcDVWHpd3LpLgboI=

Data Model 8 (release) - EqtMzvRnVZWkXwBHu4VeVGy8UyoOe+bi67KC79kphlQ=

Instead of making a version 9, and saving the original version 8 in the data model history, I just updated 8, figuring automatic migration could take care of me. Well, it couldn't, and I couldn't make a mapping between the two, because the old (beta) version of 8 was gone.

I did it that way because it was an intermediary internal build (not a release) so it wasn't a big deal, but it did throw me for a loop!

If it wasn't an internal build and I needed to make this work, I could go back to the (beta) commit and pull out that xcdatamodel file for 8 (beta), rename the (release) version to 9, then stick it into the release build and make a mapping model between 8 and 9.

However since it was just an internal beta build, we just erased and reinstalled the app on test devices. We did verify that, when going from 7 (release) to 8 (release), the migration went smoothly.