CODEWITHSUNDEEP
iosobjective-ccore-datacore-data-migration
Shuvo Joseph
Shuvo Joseph

Reputation: 912

How to Migrate an entity in Coredata where destination entity's model is just created

I have a model Version. The entity passPhrase of Version needs to be migrated to New entity passPhrase in Home model.

But the Home model is introduced in new version of database. It was not present in old xcdatamodel. How can I migrate data from 

Version.passPhrase to Home.passPhrase

Upvotes: 0

Views: 259

Answers (2)

trapper
trapper

Reputation: 12003

And the golden rule of CoreData migration is - avoid custom migration at any cost. :)

So the way to do this to use lightweight migration to add your new entity, and then just use a one off migration script to move your data over.

You can remove the passPhrase property from your Version class definition but you need to leave it in the model for now so you can still access the old data. This can be cleaned up at some time in the future when you are confident all of your users have upgraded to the newer version, or just leave it there forever.

To access the existing value during your copy just use [version valueForKey:@"passPhrase"] and then once copied clear it out the same way [version setValue:nil forKey:@"passPhrase"]

Upvotes: 1

kaushal
kaushal

Reputation: 1573

In core data, Changing Entity / Model mapping does not comes under light weight migration. You have to handle it manually by subclassing NSMigrationManager and implementing custom NSEntityMigrationPolicy.

Apple provides little documentation on the subject.Please check the Custom Core data migration with detailed example. Hope this will help.

Upvotes: 0

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