Getting runtime error when doing fast enumeration over an NSArray of entities from Core Data in iOS

Question

I have an NSArray of Objects of type NSManagedObject that are returned from a fetch result I perform in Core Data. The NSArray contains objects, as I am able to verify this after the query by printing the contents of the NSArray to the console. My problem however is that I am unable to do fast enumeration over this array using objects of the type of entity that I have retrieved from the query. The exact error I am getting at runtime is the following:

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[My_Entity_Name countByEnumeratingWithState:objects:count:]: unrecognized selector sent to instance 0xa9f0090'

My for loop that I am using doesn't even get to run because it breaks at the for loop condition:

for (MyEntityType *entityType in self.entityArray) {
...
}

The actual fetch command I use to populate the array self.entityArray is:

self.entityArray = [[Singleton sharedInstance] retrieveEntities:self.mainEntity.relationshipEntity.relationshipEntityId];

in turn, this is how my retrieveEntity method looks like:

- (NSArray *)retrieveEntities:(NSNumber *)relationshipEntityAttributeId {

    NSManagedObjectContext *context = [[DataEngine sharedInstance] managedObjectContext];
    NSError *error;

    // Create fetch request
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:ENTITY_NAME inManagedObjectContext:context];
    [fetchRequest setEntity:entity];

    // Create predicate
    NSPredicate *pred = [NSPredicate predicateWithFormat:@"relationshipEntity.relationshipAttributeId == %@", relationshipEntityAttributeId];
    [fetchRequest setPredicate:pred];

    NSArray *items = [context executeFetchRequest:fetchRequest error:&error];
    if ([items count]>0) {
        return items[0];
    } else {
        return nil;
    }
}

Why am I getting the above error?

The added code does not really help because it uses the method `retrieveEntity`, which is unknown to us (well, at least to me). — Martin R, Nov 24 '13 at 08:07

Jeffery Thomas · Answer 1 · 2013-11-25T03:46:40.707

It says what the error is in the error message.

You have a class My_Entity_Name. An instance of My_Entity_Name is assigned to the property self.entityArray. When you do for (MyEntityType *entityType in self.entityArray), it passes the -countByEnumeratingWithState:objects:count: message to the instance, and you get the unrecognized selector error.

I would look for places where the the value is assigned (either self.entityArray = … or [self setEntityArray:…]) to figure out how self.entityArray is getting the bad value. Perhaps you should post how you are doing the fetch, or if there are other ways that self.entityArray can get assigned a value.

UPDATE

I'm not sure what -[Singleton retrieveEntity:] does. It's not a class that's a part of the standard framework, and I don't know of any 3rd party library which uses such generic naming.

What I can tell you is that based on the method name -retrieveEntity:, it looks like it returns a single object not an array of objects. Usually methods that return arrays are pluralised, so I would have expected the name to be more like -retrieveEntities:.

You got an exception because is because self.entityArray doesn't contain an NSArray. The method name doesn't look like it would return an array.

Are you absolutely sure that [[Singleton sharedInstance] retrieveEntity:…] should return an NSArray? Perhaps you should post the code for -retrieveEntity:.

UPDATE

You are not returning an array.

NSArray *items = [context executeFetchRequest:fetchRequest error:&error];
if ([items count]>0) {
    return items[0];
} else {
    return nil;
}

If the items array has any elements, then the first element is returned. This is what items[0] does.

If you want to return the array change it to:

NSArray *items = [context executeFetchRequest:fetchRequest error:&error];
if ([items count]>0) {
    return items;
} else {
    return nil;
}

Notice I've replaced return items[0]; (return the first element of the array) with return items; (return the whole array).

Thanks for your answer. I've added my code showing how I populate my array from the fetch. — syedfa, Nov 24 '13 at 07:21
[Singleton retrieveEntity] is my Singleton instance which calls my method to retrieve the results from Core Data. I've changed the name as you suggested to be more accurate on its functionality (i.e. making it plural because it is supposed to return multiple results. I've also included the method that does the actual fetching. — syedfa, Nov 24 '13 at 17:28
Would I be receiving this error if I my array contained only one object? I'm asking this because if I do an NSLog:(@"Number of objects in array are: %d", [self.entityArray count]); I notice that I get the same error for this line also. — syedfa, Nov 24 '13 at 17:45

score 0 · Answer 2 · answered Nov 24 '13 at 07:50

0

There is a typo in the code, you populate self.entityAray, en draw from self.entityArray. Either this is a small typo in your example here, or it explains your error. When looking for self.entityArray it cannot find it because of the spelling error en throws the NSInalidArgumentException

answered Nov 24 '13 at 07:50

ophychius

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Thanks for pointing it out, it was a typo on my part when posting the question. – syedfa Nov 24 '13 at 17:26

Getting runtime error when doing fast enumeration over an NSArray of entities from Core Data in iOS

2 Answers2