Why is this code raising the “CoreData: error: (19) PRIMARY KEY must be unique” error?

Question

This code raises the \"CoreData: error: (19) PRIMARY KEY must be unique\" error. The Day entity has only a when attribute which is an NSDate<

Answer 1

I guess you don't need to insert a new Day if you already have it (this is the case when day is not nil). In particular I'm referring to [moc insertObject:day].

If you use insertNewObjectForEntityForName, that method inserts the object for you when you save the moc. If you need to modify it (you have retrieved a non-nil day) modify it and save. In additon, I will do processPendingChanges when the loop finishes (just for performance reasons).

Hope that helps.