CODEWITHSUNDEEP
ioscore-dataupgradeicloud
Electron
Electron

Reputation: 100

Migrating iCloud Core Data manually

I have an app that reads wind readings at sites around the world. I decided to use iCloud and Core Data using a shoe-box style app.

The wind readings update hourly, after a few weeks of using the app I realised this was a bad idea as iCloud/Core Data just fills up with megabytes of transactions and restoring a device takes 10 minutes to download the store to a fresh device.

My solution to this was to use Core Data configurations so that the "sites" were stored in the iCloud store but the hourly changing "wind readings" which get deleted after 12 hours were stored in a local store. If it makes it easier to imagine, it works similar to RSS "sites" and "entries" which change hourly.

This all works great but I can't work out how to write migration code for the 2.0 version of my app. After reading how configurations work I had to remove the parent/child relationship between sites and wind readings and use fetch requests to link them up using a common siteIdentifier UUID.

Doing it this way I assume I cannot use light-weight migrations? Also loading up the versioned .momd model file just gives me the latest model so how do I get hold of the original model file to load up the store and do everything manually.

On the other hand, is this just too complicated and I would be better removing iCloud support or there is another way you'd recommend?

Upvotes: 1

Views: 350

Answers (1)

Marcus S. Zarra
Marcus S. Zarra

Reputation: 46728

You should be able to use a lightweight migration in this situation.

The reason is, as far as your 'iCloud' configuration is concerned you are just deleting an entity and dropping a properties (i.e. dropping a table and a column). Automatic migration can handle that just fine.

However...

There is a catch. It won't copy the data you have to the 'local' configuration first. Therefore you will need to do that manually before the migration. Here are the basic steps:

  1. Determine if this migration needs to occur.
  2. Copy the sqlite file to "local.sqlite".
  3. Stand up the iCloud configuration, this will delete the readings.
  4. Stand up the local configuration, this will delete the sites.
  5. Test, test, test again, and keep testing.

Upvotes: 1

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