如何设置NSManaged变量？

Question

I have a NSManagedObject class with two relationships: courseA and courseB . These relationships should be represented in a dynamic variable. How is it possible to change this variable from outside the class?

@objc(Universtity)
    public class Universtity: NSManagedObject {

        dynamic var name: String {
            get {
                let name = self.courseA?.name
                return name!
            }
        }
    }

For example from within a ViewController like University.name = University.courseB.name ? I was thinking about a Notifikation, but this seems maybe a little more complicated as it could be.

And if there is no other way, how should I implement the observer inside the University class?

Thank you for every idea.

Answer 1

Looking at your code, you have declared a "computed" or "ready-only" variable. This is a variable whose value comes from another variable or combination of variables.

I can't see your data model, so it's not clear if you have defined a name parameter in the Core Data model. Regardless, if you have the logic is somewhat confused, because the getter you have defined means any value it may hold would be ignored anyway. You would need to define a setter to set self.courseA.name if you want to ensure the value can be written to. You don't need to worry about key-value coding notifications, because they will be triggered by the Core Data Managed Object.

public class Universtity: NSManagedObject {

    dynamic var name: String {
        get {
            let name = self.courseA?.name
            return name!
        }
        set(newValue) {
            courseA!.name = newValue
        }
    }
}

Also the pattern you have used to force unwrap a non-optional value in your getter isn't optimal. I haven't edited this because that is another discussion, but I would suggest asking yourself the question am I sure why I am doing this? for every "?" and "!" you use.