Question

I have the following entities:

• User. The common user entity with username, mail, etc.
• ComputerUserWithAI. Similar to user but it’s controlled by the application.
• Pick. Contains a relation to Game and it should hold a picker.

Since a Picker can be an User or a ComputerUserWithAI I created an Abstract Entity called Picker and I made User and ComputerWithAI extend that Picker class.
Once I added the Picker entity I made Pick have a relation to the Picker entity called picker.

Everything went fine, but I can’t insert a ComputerUserWithAI to a Pick. My code is like this:

ComputerUserWithAI *userWithAI = [NSEntityDescription insertNewObjectForEntityForName:@"ComputerUserWithAI" inManagedObjectContext:ctx];
userWithAI.name = @"DeepBlue";

Pick *pick = [NSEntityDescription insertNewObjectForEntityForName:@"Pick" inManagedObjectContext:ctx];
pick.game = game;
pick.picker = userWithAI;

The error I get is the following:

Terminating app due to uncaught exception
‘NSInvalidArgumentException’, reason: ‘Unacceptable type of value for
to-one relationship: property = “picker”; desired type = Picker; given
type = NSManagedObject; value = (entity:
ComputerUserWithAI…

But when I do:

pick.picker = [NSEntityDescription insertNewObjectForEntityForName:@"Picker" inManagedObjectContext:ctx];

it does work.

I checked the generated classes from core data and they are extending the Abstract Entity correctly. What might be wrong?

Answer 1

Found the error. The generated Pick.h had the following:

@class Picker
@interface Pick : NSManagedObject

@property (nonatomic, retain) NSManagedObject *game;
@property (nonatomic, retain) Picker *picker;

Changing it to:

@interface Pick : NSManagedObject

@property (nonatomic, retain) NSManagedObject *game;
@property (nonatomic, retain) NSManagedObject *picker;

made everything work.

Try verifying the code generated by Xcode. This happened to me using Xcode 4.2.