Core Data. How to use method created in NSManagedObject subclass

Question

My data model

I generated to subclasses Pack and Class. In Pack.m I can see the following

#import "Pack.h"
#import "Card.h"

@implementation Pack
@dynamic packTitle;
@dynamic card;

- (void)addCardObject:(Card *)value {    
    NSSet *changedObjects = [[NSSet alloc] initWithObjects:&value count:1];
    [self willChangeValueForKey:@"card" withSetMutation:NSKeyValueUnionSetMutation usingObjects:changedObjects];
    [[self primitiveValueForKey:@"card"] addObject:value];
    [self didChangeValueForKey:@"card" withSetMutation:NSKeyValueUnionSetMutation usingObjects:changedObjects];
    [changedObjects release];
}

- (void)removeCardObject:(Card *)value {
    NSSet *changedObjects = [[NSSet alloc] initWithObjects:&value count:1];
    [self willChangeValueForKey:@"card" withSetMutation:NSKeyValueMinusSetMutation usingObjects:changedObjects];
    [[self primitiveValueForKey:@"card"] removeObject:value];
    [self didChangeValueForKey:@"card" withSetMutation:NSKeyValueMinusSetMutation usingObjects:changedObjects];
    [changedObjects release];
}

- (void)addCard:(NSSet *)value {    
    [self willChangeValueForKey:@"card" withSetMutation:NSKeyValueUnionSetMutation usingObjects:value];
    [[self primitiveValueForKey:@"card"] unionSet:value];
    [self didChangeValueForKey:@"card" withSetMutation:NSKeyValueUnionSetMutation usingObjects:value];
}

- (void)removeCard:(NSSet *)value {
    [self willChangeValueForKey:@"card" withSetMutation:NSKeyValueMinusSetMutation usingObjects:value];
    [[self primitiveValueForKey:@"card"] minusSet:value];
    [self didChangeValueForKey:@"card" withSetMutation:NSKeyValueMinusSetMutation usingObjects:value];
}


@end

All those methods were generated by xcode as not public. I tried to make the first one to be a public method and write to the database this way in my viewController where inputCardPack is array of arrays.

Pack* pack = [NSEntityDescription insertNewObjectForEntityForName:@"Pack" inManagedObjectContext:self.context];
pack.packTitle = self.inputCardPackTitle;


for (int i = 0; i< [self.inputCardPack count]; i++ ){

    NSNumber *level = [NSNumber numberWithInt:0];

    Card *card = [NSEntityDescription insertNewObjectForEntityForName:@"Card" inManagedObjectContext:self.context];

    card.term = [[self.inputCardPack objectAtIndex:i] objectAtIndex:0];

    card.def = [[self.inputCardPack objectAtIndex:i] objectAtIndex:1];

    card.level = level;
    //I'm trying to add a card to pack
    [pack addCardObject:card];

}

It does not work, I'm getting an error on the last line. If I remove the last line, it works. Questions: is it right approach to use those generated methods? How to get all cards belonging to defined Pack?

yes, it is recommended to use generated method by xcode. What error are you getting ? — Leonardo
I'm getting Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSManagedObject addCardObject:]: unrecognized selector sent to instance 0x4f42f60' — Michael
The problem was with model. I deleted it before, named ii and afterwords renamed. Now I just made product -> clean and it works! The second question is still hanging on. — Michael

onetwopunch onetwopunch · Accepted Answer · 2013-01-22T18:42:10

Did you try to instantiate a new card object like this?

NSEntityDescription * description = [NSEntityDescription 
          entityForName:@"Card" inManagedObjectContext:self.context];

Card *card = [[Card alloc]initWithEntity:description 
          insertIntoManagedObjectContext:self.context];

Then once you have that temp card object, you can set values to it like so:

[card setValue: [[self.inputCardPack objectAtIndex:i] objectAtIndex:0]
      forKey: "term"];

You can go about this other ways to be sure, but because of that pesky little @dynamic identifer, the compiler takes issue with you not setting the values in the "CoreData" prescribed way. Basically, you are trying to set the value of a property that does not have space allocated for it yet because you did not @synthesize and alloc it.

I am not 100% on the inner workings of clang (the objective-c compiler) so if anyone sees problems with what I am saying, please let me know. This methodology just seems to work for me.

Hope this helps

Core Data. How to use method created in NSManagedObject subclass

1 Answers