NSManagedObjectContext helpful additions for async request execution

NSManagedObjectContext+AsyncExecute.h

#import <CoreData/CoreData.h>

@interface NSManagedObjectContext (AsyncExecute)

- (void)asyncExecuteFetchRequest:(NSFetchRequest *)request
                      completion:(void (^)(NSArray *objects, NSError *error))completion;

- (void)asyncCountForFetchRequest:(NSFetchRequest *)request
                       completion:(void (^)(NSInteger count, NSError *error))completion;

- (void)asyncExecuteBlockInBackgroundContext:(void (^)(NSManagedObjectContext *backgroundContext))block;

@end

NSManagedObjectContext+AsyncExecute.m

#import "NSManagedObjectContext+AsyncExecute.h"

@implementation NSManagedObjectContext (AsyncExecute)

- (void)asyncExecuteFetchRequest:(NSFetchRequest *)request
                      completion:(void (^)(NSArray *objects, NSError *error))completion {
    NSPersistentStoreCoordinator *coordinator = self.persistentStoreCoordinator;
    NSFetchRequestResultType resultType = [request resultType];
    
    NSManagedObjectContext *backgroundContext = [NSManagedObjectContext privateQueueManagedObjectContext];
    [backgroundContext performBlock:^{
        backgroundContext.persistentStoreCoordinator = coordinator;
        
        NSError *error = nil;
        NSArray *fetchedObjects = [backgroundContext executeFetchRequest:request error:&error];
        
        [self performBlock:^{
            if (resultType == NSManagedObjectResultType && fetchedObjects) {

                NSArray *objectIds = [fetchedObjects valueForKey:@"objectID"];
                
                NSMutableArray *objects = [[NSMutableArray alloc] initWithCapacity:[objectIds count]];
                for (NSManagedObjectID * objectID in objectIds) {
                    NSManagedObject * obj = [self objectWithID:objectID];
                    [objects addObject:obj];
                }
                
                if (completion) {
                    completion([objects copy], nil);
                }
            }
            else {
                if (completion) {
                    completion(fetchedObjects, error);
                }
            }
        }];
    }];
}

- (void)asyncCountForFetchRequest:(NSFetchRequest *)request
                       completion:(void (^)(NSInteger count, NSError *error))completion {
    NSPersistentStoreCoordinator *coordinator = self.persistentStoreCoordinator;
    
    NSManagedObjectContext *backgroundContext = [NSManagedObjectContext privateQueueManagedObjectContext];
    [backgroundContext performBlock:^{
        backgroundContext.persistentStoreCoordinator = coordinator;
        
        NSError *error = nil;
        NSInteger count = [backgroundContext countForFetchRequest:request error:&error];
        
        [self performBlock:^{
            if (completion) {
                completion(count, error);
            }
        }];
    }];
}

- (void)asyncExecuteBlockInBackgroundContext:(void (^)(NSManagedObjectContext *backgroundContext))block {
    NSPersistentStoreCoordinator *coordinator = self.persistentStoreCoordinator;
    
    NSManagedObjectContext *backgroundContext = [NSManagedObjectContext privateQueueManagedObjectContext];
    [backgroundContext performBlock:^{
        backgroundContext.persistentStoreCoordinator = coordinator;
        
        if (block) {
            block(backgroundContext);
        }
    }];
}

#pragma mark - Helpers 

+ (instancetype)privateQueueManagedObjectContext {
    return [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
}

@end