如何为CoreData中的NSManaged属性赋予初始值？

Question

I use Swift. I have a CoreData, and it has a string attribute called days. I want to assign a default value to this. I tried it in my CoreData model class but it gives an error saying "NSManaged property cannot have an initial value" .

This is what I tried.

@NSManaged var daysAvailable:String = "M"

Answer 1

It's actually really easy. Just override the awakeFromInsert method for your NSManagedObject subclass.

class Person: NSManagedObject {

    @NSManaged var name: String
    @NSManaged var age: NSNumber

    override func awakeFromInsert() {
        super.awakeFromInsert()
        setPrimitiveValue(21, forKey: "age")
        setPrimitiveValue("Bob", forKey: "name")
    }
}

According to the awakeFromInsert documentation :

If you want to set attribute values in an implementation of this method, you should typically use primitive accessor methods (either setPrimitiveValue:forKey: or—better—the appropriate custom primitive accessors). This ensures that the new values are treated as baseline values rather than being recorded as undoable changes for the properties in question.

Answer 2

Override wake form insert to initialise core data object

 Override func awakeFromInsert()
 {
   super.awakeFromInsert()
   self.daysAvailable = "M"  
  } 

check following link for more details: https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/CoreData/Articles/cdManagedObjects.html

Answer 3

If it a static value, you can set it in the CoreData model editor in xcode. No need to use 'awakeFromFetch' for that