Question

This Fetch Request takes almost 10 seconds to execute on iPhone.
The goal is to fetch 1 random thumbnail from each category.
setting fetchlimit = 1 most of the times return the same thumbnail so I have to fetch all photos from each category.

Any ideas ?

    [categoriesArray enumerateObjectsUsingBlock:^(id object, NSUInteger index, BOOL *stop) {

    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Photos"];
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"place.subcategory.category == %@", object];
    [request setPredicate:predicate];
    NSError *error;
    NSArray *photosManagedObjectsArray = [managedObjectContext executeFetchRequest:request error:&error];

    NSUInteger randomIndex = arc4random() % [photosManagedObjectsArray count];

    NSManagedObject *photoObject = [photosManagedObjectsArray objectAtIndex:randomIndex];
    UIImage *photoImage = [UIImage imageWithData:[photoObject valueForKey:@"thumbnail"]];   
    UIImage *resizedImage = [photoImage imageCroppedToFitSize:CGSizeMake(IMAGE_WIDTH, IMAGE_HEIGHT)];
    [imagesArray addObject:resizedImage];
    [objectsArray addObject:photoObject];

}];

many thanks!
Bill.

Answer 1

You don’t need to pull all your objects into an array. Just change

NSArray *photosManagedObjectsArray = [managedObjectContext executeFetchRequest:request error:&error];`
NSUInteger randomIndex = arc4random() % [photosManagedObjectsArray count];

to this

NSUInteger count = [managedObjectContext countForFetchRequest:request error:&error];
NSUInteger randomIndex = arc4random() % count;

Now use fetchOffset to grab just the single object you need.

[request setFetchOffset:randomIndex];
[request setFetchLimit:1];