bartjacobs / subclassingnsmanagedobject

Subclassing NSManagedObject

Subclassing NSManagedObject

Author: Bart Jacobs

Up until now, we've used NSManagedObject instances to represent and interact with records stored in the persistent store. This works fine, but the syntax is verbose, we lose autocompletion, and type safety is also an issue.

Remember from earlier in this series that the values of a managed object are accessed by invoking value(forKey:) and setValue(_:forKey:).

record.value(forKey: "firstName")
record.setValue("Bart", forKey: "firstName")

Because value(forKey:) returns an object of type Any?, we need to cast the result to the type we expect, using optional binding.

if let name = record.value(forKey: "name") as? String {
    print(name)
}

While we could improve these examples by replacing string literals with constants, there is an even better approach, subclassing NSManagedObject.

Read this article on Cocoacasts.