ios - 如何为 CoreData 中的 NSManaged 属性赋予初始值？

Question

我使用 Swift。我有一个 CoreData，它有一个名为 days 的字符串属性。我想为此分配一个默认值。我在我的 CoreData 模型类中尝试过它，但它给出了一个错误，提示 “NSManaged 属性不能有初始值”。

这是我试过的。

@NSManaged var daysAvailable:String = "M"

Answer 1

其实很简单。只需覆盖 NSManagedObject 子类的 awakeFromInsert 方法即可。

class Person: NSManagedObject {

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

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

根据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.