CODEWITHSUNDEEP
iosswiftxcodecore-dataswift3
MeMTn
MeMTn

Reputation: 93

Core Data Unique constraint except for the default value

I have an entity called "Person". it has an attribute "id" with a default value = 0. I have set a constraint in "Person" to have only unique Ids. I am loading a list of Persons from the server and storing them locally using core data. The Person ids should be unique, but when I create multiple persons locally I want the uniqueness of id to be ignored if it has the default value 0.

I just want the uniqueness constraint to work on every id different then 0, how can I do this?

thanks,

Upvotes: 2

Views: 1639

Answers (2)

Jon Rose
Jon Rose

Reputation: 8563

Before constraints where add to core-data the only way to insure uniqueness is to do a fetch and then if there are no results create the object. It is not that difficult to do. Enforce uniqueness in you code and use whatever custom logic you need. Try to organize you code so that there are only one or two ways to create a person so the logic is easier to handle.

Upvotes: 0

Tom Harrington
Tom Harrington

Reputation: 70966

Core Data's uniqueness constraints are just that-- they require uniqueness, without exceptions. Your situation of wanting "unique except for one value that can be duplicated" isn't directly supported by Core Data. You'd have to maintain that in your own code somehow. That probably means implementing your own update-or-insert logic to check whether an ID exists. That would be something like,

  1. Do a fetch with the specific ID.
  2. If you find an object update it.
  3. If you don't find an object, create a new one.

Upvotes: 2

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