Why is the + initialization method of objects controlled by master data called twice?

Question

I have a managed main data object using a method +initialize. (If that matters, I want to use this method to initialize a static variable, which is expensive to set up.) When testing this initialization code, I was surprised to find that the method +initializegets called twice.

The first call initialize selfdefines how (Class) MyClass, as one would expect.

The second time initializeit selfis called is defined as (Class) MyClass_MyClass_, which makes me suspect some kind of unusual initialization for objects managed by Core Data.

Although this does not pose a problem for me (I can just check if the static variable was initialized, which I would do to handle ubclassing), it makes me suspect that Core Data is doing something in the life cycle of an object or class that I do not understand. Can someone explain to me what happens in this method call MyClass_MyClass_ +initialize?

Answer 1

Access methods for master data properties are dynamically generated at run time. This works by creating a subclass MyClass_MyClass_(of MyClass) and adding the necessary methods for the subclass.

Core Data , :

e = [NSEntityDescription insertNewObjectForEntityForName:@"MyClass" inManagedObjectContext:context];
NSLog(@"%@", [e class]);               // --> MyClass
NSLog(@"%s", object_getClassName(e));  // --> MyClass_MyClass_

, , .

NSLog(@"%@", [e class]);               // --> NSManagedObject
NSLog(@"%s", object_getClassName(e));  // --> NSManagedObject_MyClass_

e " " NSManagedObject, NSManagedObject_<EntityName>_. ( ).

Answer 2

NSObject , : , , , . . . , - , [super initialize]. , ...

+ (void)initialize {
    if (self == [ClassName class]) {
    // ... do the initialization ...
   }
}

awakeFrom... NSManagedObject ?