CoreDataStack

How to initialize a core-data-context using CoreDataStack:

//Lets say you have a core-data model named: CoreDataTest.xcdatamodeld file
//where usually all models are laied down.
//Using CoreDataStack that's like this:
NSManagedObjectContext *context = [[NGKeyedContext sharedInstance] contextForKey:@"CoreDataTest"];

//Now we have an context, so how do we read rows from the context of an perticular Entity named: Photo.h
//Write just this:
NSArray *temps = [Photo read:nil context:context];

//Insted of doing this: (Too much boilerplate code need to write for a simple work)
NSFetchRequest *request = [[NSFetchRequest alloc] init];
request.entity = [NSEntityDescription entityForName:@"Photo" inManagedObjectContext:context];
NSError *error;
NSArray *temps = [context executeFetchRequest:request error:&error];
//

//Insert New Photo object into context: using methods form NGManagedObjectProtocol
//we have 2 verient: using NSDictionary or NSData
//e.g. -insertIntoContext:(NSManagedObjectContext) withProperties:(NSDictionary)
// or  -insertIntoContext:(NSManagedObjectContext) withJSON:(NSData*)

//On success of insertion new object will return
Photo *photo = [Photo insertIntoContext:context 
                      withProperties:@{@"location":location
                                      ,@"title":@"Mount Everest"
                                      ,@"photoId":[NSUUID UUID].UUIDString
                                      ,@"datetimeAtTook":[NSDate date]}];

//We know update/delete relatively easy using context.

//For updating..
//first find the Object, using -read:(NSDictionary) context:(NSManagedContext) api:
//where we can provide search criteria for an object: e.g. finding photo by title = @"photo-title"
//
NSArray* photos = [Photo read:@{@"title":@"Mount Everest"} context:context];
Photo *photoToUpdate = photos[0];
//..update
[context save:nil];

//For Deleting..
[context deleteObject: photoToUpdate];

###How to deal with multiple-context: ####.e.g one context for main-thread others are for background thread

/**
 * Calling -mergeContextForKey:fromContext: from main-queue will causes certain crash.
 * Background-context must be created in backgroud queue, using -cloneContextForKey: method.
 * After that merge that context with other context tracked by NGKeyedContext.
 */
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0);
dispatch_async(queue, ^{
    NSManagedObjectContext *bgContext = [[NGKeyedContext sharedInstance] cloneContextForKey:@"CoreDataTest"];
    //Writing new entity into the background context:
    NSUInteger count = [Photo rows:backbgoundContext];
    NSLog(@"RowCount : %ld",(long)count);
    // -insertIntoContext:withProperties will insert a new Photo instance into the context and
    //return the newly created onject.
    Photo *photo = [Photo insertIntoContext:bgContext
                            withProperties:@{@"location":location
                                           ,@"title":@"K2 peak"
                                           ,@"photoId":[NSUUID UUID].UUIDString
                                           ,@"datetimeAtTook":[NSDate date]}];
    assert(photo);
    //Finally merge the current change with other context:
    [[NGKeyedContext sharedInstance] mergeContextForKey:@"CoreDataTest" fromContext:backbgoundContext];
});