Core data model versioning and data migration apple developer

William Boles

core data model versioning and data migration apple developer

iOS Core Data with Swift

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There are very few certainties in app development, but one is that once your app is released it will change in unexpected ways. And no matter how flexible your architecture is inevitably one of those changes will be a breaking change. Perhaps the most important breaking changes involve the user's data. If your app loses or corrupts user data you can expect at least some reputational damage and if the loss is severe enough you can end up doing your competitors marketing for them by turning your users into their users. If you have any doubt about the impact of data loss imagine how you would feel if a game you had been playing was updated and deleted your recently hard earned thingamabob - all that time and effort lost through no fault of yours. And that's just a game, now imagine how your users would feel when your far-more-important app starts losing their data.

This is an abridged chapter from our book Core Data by Tutorials , which has been completely updated for Swift 4. This tutorial is presented as part of our iOS 12 Launch Party enjoy! During app development, well before the ship date, thorough testing can help iron out the data model. What do you do then? The migration process will update data created with a previous version of the data model to match the current data model.

You define this information first in the Core Data model, then use it to generate a schema for CloudKit. As you design your model, note the following limits of the CloudKit schema and make sure you design a compatible model. All relationships must be optional. Due to operation size limitations, relationship changes may not be saved atomically. All relationships must have an inverse, in case the records synchronize out of order. In a Core Data model, an inverse is strongly recommended but not required.



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Core Data provides support for managing changes to a managed object model as your application evolves. - As developers, we constantly try to improve our apps by adding features and optimizing the code. Sometimes these changes have an impact on the data model.

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