CoreData singleton

gistfile1.m

//
//  CoreDataManager.h
//
//  Created by Rex Fatahi on 3/17/14.
//  Copyright (c) 2014 aug2uag. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface CoreDataManager : NSObject

@property (nonatomic, retain, readonly) NSManagedObjectModel *managedObjectModel;
@property (nonatomic, retain, readonly) NSManagedObjectContext *managedObjectContext;
@property (nonatomic, retain, readonly) NSPersistentStoreCoordinator *persistentStoreCoordinator;

+ (CoreDataManager *)sharedInstance;
- (NSManagedObjectContext *) managedObjectContext;
- (NSArray *)returnAllChannelsCreated;
- (NSArray *)returnAllChannelsFollowed;

@end

gistfile2.m

//
//  CoreDataManager.m
//
//  Created by Rex Fatahi on 3/17/14.
//  Copyright (c) 2014 aug2uag. All rights reserved.
//

#import "CoreDataManager.h"
#import <CoreData/CoreData.h>

@implementation CoreDataManager

@synthesize managedObjectContext = _managedObjectContext;
@synthesize managedObjectModel = _managedObjectModel;
@synthesize persistentStoreCoordinator = _persistentStoreCoordinator;

static CoreDataManager* sharedInstance = nil;

+ (CoreDataManager *)sharedInstance
{
    if (sharedInstance == nil) {
        static dispatch_once_t onceToken;
        dispatch_once(&onceToken, ^{
            sharedInstance = [[CoreDataManager alloc] init];
        });
    }
    
    return sharedInstance;
}

// 1
- (NSManagedObjectContext *) managedObjectContext {
    
    
    // to delete all entries in Core Data
    /*
    NSArray *stores = [_persistentStoreCoordinator persistentStores];
    for(NSPersistentStore *store in stores) {
        [_persistentStoreCoordinator removePersistentStore:store error:nil];
        [[NSFileManager defaultManager] removeItemAtPath:store.URL.path error:nil];
    }
    
    _persistentStoreCoordinator = nil;
     */
    
    if (_managedObjectContext != nil) {
        return _managedObjectContext;
    }
    NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
    if (coordinator != nil) {
        _managedObjectContext = [[NSManagedObjectContext alloc] init];
        [_managedObjectContext setPersistentStoreCoordinator: coordinator];
    }
    
    return _managedObjectContext;
}

//2
- (NSManagedObjectModel *)managedObjectModel {
    if (_managedObjectModel != nil) {
        return _managedObjectModel;
    }
    _managedObjectModel = [NSManagedObjectModel mergedModelFromBundles:nil];
    
    return _managedObjectModel;
}

//3
- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {
    
    if (_persistentStoreCoordinator == nil) {
        
        NSURL *storeUrl = [NSURL fileURLWithPath: [[self applicationDocumentsDirectory] stringByAppendingPathComponent: @"pcApp"]];
        NSError *error = nil;
        _persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc]
                                       initWithManagedObjectModel:[self managedObjectModel]];
        if(![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType
                                                      configuration:nil URL:storeUrl options:nil error:&error]) {
            /*Error for store creation should be handled in here*/
        }
    }
    
    return _persistentStoreCoordinator;
}

//4
- (NSArray*)returnAllChannelsCreated
{
    // initializing NSFetchRequest
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    
    //Setting Entity to be Queried
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Channel"
                                              inManagedObjectContext:self.managedObjectContext];
    [fetchRequest setEntity:entity];
    NSError* error;
    
    // Query on managedObjectContext With Generated fetchRequest
    NSArray *fetchedRecords = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];
    
    // Returning Fetched Records
    return fetchedRecords;
}

//5
- (NSArray *)returnAllChannelsFollowed
{
    // initializing NSFetchRequest
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    
    //Setting Entity to be Queried
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Follow"
                                              inManagedObjectContext:self.managedObjectContext];
    [fetchRequest setEntity:entity];
    NSError* error;
    
    // Query on managedObjectContext With Generated fetchRequest
    NSArray *fetchedRecords = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];
    
    // Returning Fetched Records
    return fetchedRecords;
}

- (NSString *)applicationDocumentsDirectory {
    return [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
}

@end