Question

Does a setter of a CoreData-attribute retains? or copies the value or what does the setter? I want to know if I have to (auto-)release the value that I am putting into the setter.

I’ve done some quick tests on that. Assuming the following model:

+----------+
| Class A  |
+----------+
| v :int32 |
+----------+

The generated ManagedObject then looks like this:

//A.h
@interface A :  NSManagedObject  
{
}
@property (nonatomic, retain) NSNumber * v;
//...

//A.m
@implementation A 
@dynamic v;
...

Ok, the property is marked with retain, so if I set a NSNumber to v the NSNumber should be retained. but it is not (I think). I did the following:

A *a = ... ;
NSNumber *retainCheck = [[NSNumber alloc] initWithInt:23];
NSLog(@"retainCheck1: %i",[retainCheck retainCount]);
a.v = retainCheck;
NSLog(@"retainCheck2: %i",[retainCheck retainCount]);
NSLog(@"retainCheck3: %i",[a.v retainCount]);
NSLog(@"pointer1: %#x",retainCheck);
NSLog(@"pointer2: %#x",a.v);

this produces the following output:

retainCheck1: 1
retainCheck2: 1
retainCheck3: 1
pointer1: 0x62f068
pointer2: 0x62f068

Both NSNumbers are the same NSNumber-instance (same pointer-value -> so it does no copy or sth like that) and the NSNumber doesn’t seem to be retained by the setter.

Am I doing sth. wrong in my test? or is the behaviour of NSManagedObject-setters not the same as described in the header?

edit: I am calling retainCount because I wanted to observer a retain not release or autorelease. The observed behaviour can be explained by the flyweight-pattern linked by Abizern

Answer 1

Firstly – Don’t worry about how Core Data manages it’s properties – As long as you release the objects that you own, that’s what matters.

Secondly – you’re testing using NSNumber. NSNumber is a strange class that adopts the flyweight design pattern, so getting the retainCount of an NSNumber isn’t going to tell you anything about how Core Data manages its objects.