源自 NEW- CoreData for Swift Development (Swift 4.2 & iOS 12)

Codegen: Class Definition

Class Definition automatically creates the NSManagedObject subclass behind the scene, including the attributes information.

Codegen: Category/Extension

Category/Extension allow flexibility of using the class file to handle custom function, whereas the properties file is still created and loaded behind the scene.

在使用这种模式的情况下，添加类的自定义函数时，需要手工创建该类的（Movie）的 extension 文件 Movie+CoreDataClass.swift，手动新建该类，如下截图所示。



如果忘记了 @objc(Movie) 会报错 An NSManagedObject of class 'Movie.Movie' must have a valid NSEntityDescription。