How to run simultaneous searches in core-data?

Question

I am trying to understand how to run simultaneous searches in core-data.

Here is my example, but it doesn't work, because one of the GCDs seems to never activate If I leave the custon MOC in there I get an error "unable to find model for entity 'Recipe''

-(void)performSearch:(NSString*)name{

    //TODO: Is there a better way

    //In case the previous search hasn't finished
    if (globaDispatchRequestInprogress) {
        //Send on GCD
        dispatch_queue_t searchQueque = dispatch_queue_create("search queque 2", NULL);
        dispatch_async(searchQueque, ^{
            NSLog(@"\n\nDispatch 2 In Progress*******\n\n");


            //Init local variables
            NSFetchRequest *fetchRequest =[[NSFetchRequest alloc]init];
            NSError *error;


             //Create own MOC for multiThread
             NSManagedObjectContext *tempContext = [[NSManagedObjectContext alloc]init];

             [tempContext setPersistentStoreCoordinator:[self persistentStoreCoordinator]];


            NSPredicate *recipeName = [NSPredicate predicateWithFormat:@"ANY recipe.name ==[c] %@",name];

            //Set predicate to fetch request
            [fetchRequest setPredicate:recipeName];

            //Set query. We are searching recipes
            NSEntityDescription *entity = [NSEntityDescription entityForName:@"Recipe" inManagedObjectContext:tempContext];
            //sets up fetch request details
            [fetchRequest setEntity:entity];

            //Attempt to speed up program
            [fetchRequest setReturnsObjectsAsFaults:NO];


            //Perform fetch assign to return array
            NSArray*records = [tempContext executeFetchRequest:fetchRequest error:&error];

            //Add to temporary results
            //TODO: Add to NSDictionary
            [self addResultsToTemporaryResults:records];

            NSLog(@"Total results = %i",[_temporaryResultsArray count]);

            NSLog(@"\n\nDispatch 2 END**************\n\n");

        });

    }
    //Send on GCD
    dispatch_queue_t searchQueque = dispatch_queue_create("search queque", NULL);
    dispatch_async(searchQueque, ^{
        NSLog(@"\n\nDispatch In Progress*******\n\n");

        //Set flag
        globaDispatchRequestInprogress=YES;

        //Init local variables
        NSFetchRequest *fetchRequest =[[NSFetchRequest alloc]init];
        NSError *error;


         //Create own MOC for multiThread
         NSManagedObjectContext *tempContext = [[NSManagedObjectContext alloc]init];

         [tempContext setPersistentStoreCoordinator:[self persistentStoreCoordinator]];

        NSPredicate *recipeName = [NSPredicate predicateWithFormat:@"ANY recipe.name ==[c] %@",name];

        //Set predicate to fetch request
        [fetchRequest setPredicate:recipeName];

        //Set query. We are searching recipes
        NSEntityDescription *entity = [NSEntityDescription entityForName:@"Recipe" inManagedObjectContext:tempContext];
        //sets up fetch request details
        [fetchRequest setEntity:entity];

        //Attempt to speed up program
        [fetchRequest setReturnsObjectsAsFaults:NO];

        //Perform fetch assign to return array
        NSArray*records = [tempContext executeFetchRequest:fetchRequest error:&error];

        //Add to temporary results
        //TODO: Add to NSDictionary
        [self addResultsToTemporaryResults:records];

        NSLog(@"Total results = %i",[_temporaryResultsArray count]);
        globaDispatchRequestInprogress=NO;

        NSLog(@"\n\nDispatch END**************\n\n");

    });

}

Answer 1

I see several things that make me suspicious, but no obvious smoking gun.

If you're seeing "unable to find model", that suggests that your persistent store coordinator is not being configured the way you think it is. It would be interesting to NSLog self.persistentStoreCoordinator.managedObjectModel, and also self.persistentStoreCoordinator.managedObjectModel.entitiesByName.

The preferred GCD approach to Core Data is to use performBlock: or performBlockAndWait:, with the proper concurrency type for your managed object context. See http://developer.apple.com/library/mac/#releasenotes/DataManagement/RN-CoreData/index.html

You're keeping the results of your fetch around, in your addResultsToTemporaryResults: call. We don't see the source for it, but is it thread-safe? Those records you found have no existence outside of the tempContext you fetched them in, and may only be accessed from the thread that found them. You probably want to be using NSManagedObjectIDs there (and perhaps you already are).

Your second call to dispatch_queue_create() will always be executed. Did you mean to do an if-else instead of a simple if?

When you do -executeFetchRequest:error:, check the result. If it's a nil result, take a look at the NSError you passed in.