A class that encapsulates setting up a Core Data stack, separating this function from the rest of a Cocoa application, particularly from the Application Delegate. This was inspired/copied from NSScreencast.com episode 11.

PJSDatModel.h

//
//  PJSDatModel.h
//  PJSBoilerplate
//
//  Created by Rob Feldmann on 8/8/13.
//  Copyright (c) 2013 PajamaSoft, LLC. All rights reserved.
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in
//  all copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
//  SOFTWARE.
//
//  Inspiration: http://nsscreencast.com/episodes/11-core-data-basics

#import <Foundation/Foundation.h>

@interface PJSDataModel : NSObject

@property (nonatomic, readonly) NSManagedObjectContext *mainContext;
@property (nonatomic, readonly) NSPersistentStoreCoordinator *persistentStoreCoordinator;
@property (nonatomic) BOOL supportsUndo; //Default = NO

#pragma mark - Class Methods

+ (instancetype)sharedDataModel;

#pragma mark - Instance Methods

- (NSString *)modelName;
- (NSString *)pathToModel;
- (NSString *)storeFilename;
- (NSString *)pathToLocalStore;

@end

PJSDatModel.m

//
//  PJSDatModel.m
//  PJSBoilerplate
//
//  Created by Rob Feldmann on 8/8/13.
//  Copyright (c) 2013 PajamaSoft, LLC. All rights reserved.
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in
//  all copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
//  SOFTWARE.
//
//  Inspiration: http://nsscreencast.com/episodes/11-core-data-basics

#import "PJSDataModel.h"

@interface PJSDataModel ()

@property (nonatomic, strong) NSManagedObjectModel *managedObjectModel;

- (NSString *) documentsDirectory;

@end

@implementation PJSDataModel

@synthesize mainContext = _mainContext;
@synthesize persistentStoreCoordinator = _persistentStoreCoordinator;

#pragma mark - Class Methods

+ (instancetype)sharedDataModel {
    static dispatch_once_t once;
    static PJSDataModel *__instance;
    dispatch_once(&once, ^{
        __instance = [[PJSDataModel alloc] init];
        __instance.supportsUndo = NO;
    });
    return __instance;
}

#pragma mark - Paths

- (NSString *)modelName {
    return @"PJSDataModel";
}

- (NSString *)pathToModel {
    return [[NSBundle mainBundle] pathForResource:[self modelName]
                                           ofType:@"momd"];
}

- (NSString *)storeFilename {
    return [[self modelName] stringByAppendingPathExtension:@"sqlite"];
}

- (NSString *)pathToLocalStore {
    return [[self documentsDirectory] stringByAppendingPathComponent:[self storeFilename]];
}

- (NSString *)documentsDirectory {
    static NSString *documentsDirectory = nil;
    if (documentsDirectory == nil) {
        NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        documentsDirectory = [paths objectAtIndex:0];
    }
    return documentsDirectory;
}

#pragma mark - Accessors

- (NSManagedObjectContext *)mainContext {
    if (_mainContext == nil) {
        _mainContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
        _mainContext.persistentStoreCoordinator = [self persistentStoreCoordinator];
    }
    
    return _mainContext;
}

- (NSManagedObjectModel *)managedObjectModel {
    if (_managedObjectModel == nil) {
        NSURL *storeURL = [NSURL fileURLWithPath:[self pathToModel]];
        _managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:storeURL];
    }
    
    return _managedObjectModel;
}

- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {
    if (_persistentStoreCoordinator == nil) {
        DDLogCVerbose(@"SQLITE STORE PATH: %@", [self pathToLocalStore]);
        NSURL *storeURL = [NSURL fileURLWithPath:[self pathToLocalStore]];
        NSPersistentStoreCoordinator *psc = [[NSPersistentStoreCoordinator alloc]
                                             initWithManagedObjectModel:[self managedObjectModel]];
        NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
                                 [NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption,
                                 [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil];
        NSError *e = nil;
        if (![psc addPersistentStoreWithType:NSSQLiteStoreType
                               configuration:nil
                                         URL:storeURL
                                     options:options
                                       error:&e]) {
            NSDictionary *userInfo = [NSDictionary dictionaryWithObject:e forKey:NSUnderlyingErrorKey];
            NSString *reason = @"Could not create persistent store.";
            NSException *exc = [NSException exceptionWithName:NSInternalInconsistencyException
                                                       reason:reason
                                                     userInfo:userInfo];
            @throw exc;
        }
        
        _persistentStoreCoordinator = psc;
    }
    
    return _persistentStoreCoordinator;
}

- (void)setSupportsUndo:(BOOL)supportsUndo {
    if (supportsUndo) {
        self.mainContext.undoManager = [[NSUndoManager alloc] init];
    } else {
        self.mainContext.undoManager = nil;
    }
}

@end

PJSDatModelTests.m

//
//  PJSDatModelTests.m
//  PJSBoilerplate
//
//  Created by Rob Feldmann on 9/22/13.
//  Copyright (c) 2013 PajamaSoft, LLC. All rights reserved.
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in
//  all copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
//  SOFTWARE.
//

#import <XCTest/XCTest.h>
#import "PJSDataModel.h"

@interface PJSDatModelTests : XCTestCase

@property (nonatomic, strong) PJSDataModel *dataModel;

@end

@implementation PJSDatModelTests

- (void)setUp
{
    [super setUp];
    self.dataModel = [PJSDataModel sharedDataModel];
}

- (void)tearDown
{
    // Put teardown code here; it will be run once, after the last test case.
    [super tearDown];
}

-(void)testDataModelInstantiation {
    XCTAssertNotNil(self.dataModel, @"dataModel should not be nil");
}

-(void)testSingletonBehavior {
    PJSDataModel *one = [PJSDataModel sharedDataModel];
    PJSDataModel *two = [PJSDataModel sharedDataModel];
    
    XCTAssertEqualObjects(one, two, @"singleton instances should be equal");
}

-(void)testPaths {
    XCTAssertNotNil(self.dataModel.pathToModel, @"pathToModel should not be nil");
    XCTAssertNotNil(self.dataModel.storeFilename, @"storeFilename shold not be nil");
    XCTAssertNotNil(self.dataModel.pathToLocalStore, @"pathToLocalStore should not be nil");
}

-(void)testPersistentStoreCoordinatorProperty {
    NSPersistentStoreCoordinator *psc = self.dataModel.persistentStoreCoordinator;
    XCTAssertNotNil(psc, @"persistent store coordinator should not be nil");
}

-(void)testMainContextProperty {
    NSManagedObjectContext *context = self.dataModel.mainContext;
    
    XCTAssertNotNil(context, @"mainContext should not be nil");
    
    XCTAssertTrue(context.concurrencyType == NSMainQueueConcurrencyType,
                  @"mainContext should be on the main thread");
    
    XCTAssertEqual(context.persistentStoreCoordinator,
                   self.dataModel.persistentStoreCoordinator,
                   @"mainContext's persistentStoreCoordinator property should be equal to dataModel's psc");
}

@end