Question

I have 3 entities that I generated with MOGenerator, I’d like to be able to get one of them back from their objectID

I tried this :

- (void)aMethod: (SpecialEntity1ID *)entityID
{
    //This is a method from MagicalRecord but it doesn't matter(I think...).
    NSManagedObjectContext *context = [NSManagedObjectContext MR_contextWithParent:[NSManagedObjectContext MR_defaultContext]];

    SpecialEntity1 *entity1 = [context objectRegisteredForID:entityID]
    //But this returns an NSManagedObject so it doesn't work...
}

Could someone help me get this object back with its ID ?

Since I don’t know how to do it with the ID I’m currently working around it by making a method with an NSStringas a paramater instead of SecialEntity1ID that defines one of the attribute of this object (and is unique) and fetching the object.

I think getting back with his ID is better so any idea ?

Answer 1

You want to use existingObjectWithID:error: method of your NSManagedObjectContext and typecast the return type if you are 100% sure what it will be. I’d keep it generic i.e. let it return an NSManagedObject and then test its class elsewhere if you want to determine whether it belongs to a particular class.

- (Object*)retrieveObjectWithID:(ObjectID*)theID
{
    NSError *error = nil;
    Object *theObject = (Object*)[[NSManagedObjectContext contextForCurrentThread] existingObjectWithID:theID error:&error];
    if (error)
        NSLog (@"Error retrieving object with ID %@: %@", theID, error);
    return theObject;
}