问题
I am new to core data and iphone programming so dont mind my silly qn. I couldn't figure out how to mark a attribute as a primary key in the xcdatamodel file or may be outside. I looked around and found some people saying that it is not possible.
I am getting identifier for every object that i am getting, i would need to store that object through core data and i might need to use that identifier in my web service to retrieve additional data. How do i keep the primary key of an entity equal to that identifier, any help is greatly appreciated.
Thanks in advance,
Yogesh
回答1:
In short you cannot mark an attribute as primary key automatically. You have maintain one by your own.
You can do anyone of the below:
Use [NSManagedObject objectID].
Your own primary key-like system that stores an integer in your model and increments it with the creation of each object
回答2:
You shouldn't be thinking about Core Data as a database structure with tables and keys. That's just an implementation detail.
To get an entity with a partucular you create a fetch request into your data store for that identifier and it will retrieve that object into a managed object context.
If you are worried about performance, you can make the attribute that stored this identifiers as indexed in the data model.
来源：https://stackoverflow.com/questions/10189696/how-to-create-unique-identifier-for-an-entity-in-iphone-core-data