CoreData - Unrecognized selector when retrieving entities by their ObjectID

Question

I'm developing an application that uses multiple threads to do some intensive calculations as well as fetch a good size of data. Thus, I'm trying to be a good little developer and adhere to Apple's concurrency guidelines when designing my application with CoreData. Basically, I have an NSOperation that runs and fetches the data. It returns (to a method in the main thread) an NSMutableSet that contains an NSManagedObjectID for each of the entities returned.

Here is the method in the main thread where I want to convert those NSManagedObjectIDs to actual NSManagedObject subclasses again:

-(void)updateLocalContextWithObjectIDs:(NSMutableSet *)idSet {

    NSMutableSet *entitySet = [[NSMutableSet alloc] init];

    for (NSManagedObjectID *objectID in idSet) {

        [entitySet addObject: (Person *)[[self.dataProvider sharedManagedObjectContext] objectWithID:objectID]];

    }

    self.entitySet = entitySet;
    [entitySet release];

}

The problem I'm having is that I'm getting the following error when this loop runs:

-[Person persistentStore]: unrecognized selector sent to instance 0x619b270

Any ideas why this is happening? Calling persistentStore on the Person object isn't being done by me---it must be happening within CoreData and I'm not doing something correctly.

Thanks in advance.

Answer 1

The issue was that I was passing in a set of NSManagedObjects instead of the set of NSManagedObjectIDs like I should've been.

This is solved.

Answer 2

How to solve the "unrecognized selector sent to instance 0xXXXX bug"

1. Look for where you called persistantStore in your code. Then find where you over-released that object.

2. If you can't find where you are over releasing the object, run Instruments with NSZombies ON

Explanition: Even though your code is not calling persistantStore on a Person, your computer is. Objective-C is a dynamic language, you're computer has a pointer to a Person object and it's sending persistantStore to that object. This usually happens when you over released something that you shouldn't have. The object has gone away and a new object has replaced it, however the pointer remains, so when you send a message to that pointer, it goes to the object that now occupies that place in memory.