Core Data Primary Key

iphone cocoa-touch core-data
Mugunth picture Mugunth · May 23, 2009 · Viewed 51.3k times · Source

This may seem stupid, but I still couldn't figure out how to mark a attribute as a primary key in the xcdatamodel file. My persistent storage is sqlite file. Can anyone help me?

In that case, how can I "validate" a ID to be unique? Should I write a validation method or something?

Answer

Mike Abdullah picture Mike Abdullah · May 24, 2009

Your options are:

  • Use -[NSManagedObject objectID]. Note that this ID is temporary until either the object is saved for the first time or you call -[NSManagedObjectContext obtainPermanentIDsForObjects:error:]
  • Use the CFUUID family of functions to generate a UUID for each object in your -awakeFromInsert method
  • Create your own primary key-like system that stores an integer in your model and increments it with the creation of each object

There is no good way to validate that a property is unique. The closest you'll get is to ensure it is unique at creation time, and then implement a custom setter method that stops anyone ever changing the ID.

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