Question

I have an app with a pre populated DB. I just tried the first migration and it works great.

My Question Is

Do I need to rebuild the pre populated DB if the changes are only in the model, but not is the DB (changes is with dynamic properties that are “empty” in the pre populated DB) ?

Will the migration take effect on the pre populated DB ?

It is working with no crashes now but I wish to know that there are no side effects that I should be aware of.

Answer 1

You are just doing a lightweight migration, that’s why it’s working normally.

I’m guessing the changes in your model were not too severe, and the lightweight migration is therefore perfectly adaptable.

This means that right now you have both the old model and the new model in your project (if you expand the model). If not this should not work. Just make sure that you keep the old original model still in your project or else the migration won’t know how to proceed.

The main side effect is that as your model evolves you might no longer be able to do a lightweight migration, but I would suggest crossing that bridge if you ever get to it.

Also another side effect is that the migration is slightly slower than if you had your persistant object coordinator directly (in the order of milliseconds). There is also the remote possibility of a failure (but I can only see this happening if you can’t write to disk because the migration made your db bigger and then it couldn’t save because of insufficient disk space, but when would that ever happen 😛 )

For me personally I would rebuild my DB if it was quick before shipping as the last thing to do, but if I was on a deadline I wouldn’t since the benefits of avoiding this type of migration are not that huge.