我是否需要进行大量迁移以修改核心数据中的关系？

Question

My app loads user info from my backend and then attempts to save everything using core data. I have a couple of entities, and some one to many relationships in my data model. My question is, if the data changes in my database, and I need to modify the relationships between entities, for example add/delete, do I need to do a heavy migration? I have searched and read a lot online, it seems like lightweight migration is not gonna do it because I'm not manually adding attributes/entities. And if I do need to do a heavy migration, how would one go about that? There is really not too much I could find about heavy migration out there.

I also thought of just deleting previous data models every time I make a change then save the entire new entity. I'm not so sure if that is a good approach, is there a better way to cache/store data that's retrieved from backend?

Answer 1

If you are not changing the model you need no migration.

That is, "migration" in the sense that Apple uses it, ie only in reference to the data model . What you mean is perhaps a data "update".

You do data updates in the usual way: fetch the objects you want to modify, change them (eg, set different objects as relationships), save.

Answer 2

Probably you have done this but in case you haven't, when you change the model you need to save as a new version then select that one as current version with that the error should go away.

Here are the steps:

1. Select Model.xcdatamodeld.
2. Click Editor > Add Model Version....
3. Click Finish to accept Model 2 as the version name.
4. Select Model.xcdatamodeld.
5. Click View > Utilities > Show File Inspector (or press Option+⌘+1).
6. Set the Current Model Version to Model 2.

Here a link with explains this process: Learning CoreData for iOS: Managed Object Model Migration