Xcode中的多个xcdatamodel文件

Question

我的项目（用于管理学生参加各种课程）包含2个xkcddatamodel文件，一个用于学期开始/结束日期，另一个用于课程数据。如果您查看AppDelegate.m，我会将modelURL设置为第二个模型。我该如何为第一个xkcddatamodel创建第二个上下文？我已经尝试了here给出的解决方案。但没有骰子。 Xcode甚至没有认出它，并要求我用managedObjectContext2替换managedObjectContext。我该如何解决这个问题？

项目的Dropbox链接：https://www.dropbox.com/sh/ivl6nw6nw8p9j1y/MDwYDaHVH_

这是AppDelegate.m

//
//  AppDelegate.m
//  timetable app
//
//  Created by Robin Malhotra on 22/12/13.
//  Copyright (c) 2013 Robin's code kitchen. All rights reserved.
//

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

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    // Override point for customization after application launch.
    return YES;
}

// Explicitly write Core Data accessors
- (NSManagedObjectContext *) managedObjectContext {
    if (managedObjectContext != nil) {
        return managedObjectContext;
    }
    NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
    if (coordinator != nil) {
        managedObjectContext = [[NSManagedObjectContext alloc] init];
        [managedObjectContext setPersistentStoreCoordinator: coordinator];
    }

    return managedObjectContext;
}

- (NSManagedObjectModel *)managedObjectModel {
    if (managedObjectModel != nil) {
        return managedObjectModel;
    }
    // removed some code about retain here as ARC hates that

    return managedObjectModel;
}

- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {
    if (persistentStoreCoordinator != nil) {
        return persistentStoreCoordinator;
    }
    NSURL *storeUrl = [NSURL fileURLWithPath: [[self applicationDocumentsDirectory]
                                               stringByAppendingPathComponent: @"Courses.sqlite"]];


    NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"ClassesAttended" withExtension:@"momd"];
    managedObjectModel=[[NSManagedObjectModel alloc]initWithContentsOfURL:modelURL];

    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;
}

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

/* (...Existing Application Code...) */

-(NSArray *)getAllCourses
{
    NSFetchRequest *request=[[NSFetchRequest alloc]init];
    NSEntityDescription *entitydesc=[NSEntityDescription entityForName:@"Course" inManagedObjectContext:managedObjectContext];
    [request setEntity:entitydesc];
    NSError *error;
    NSArray *fetchedCourses=[self.managedObjectContext executeFetchRequest:request error:&error];
    return fetchedCourses;
}

@end

这是AppDelegate.h

#import <UIKit/UIKit.h>

@interface AppDelegate : UIResponder <UIApplicationDelegate>
{
    NSManagedObjectModel *managedObjectModel;
    NSManagedObjectContext *managedObjectContext;
    NSPersistentStoreCoordinator *persistentStoreCoordinator;
}

@property (strong, nonatomic) UIWindow *window;
@property (nonatomic, readonly) NSManagedObjectModel *managedObjectModel;
@property (nonatomic, readonly) NSManagedObjectContext *managedObjectContext;
@property (nonatomic, readonly) NSPersistentStoreCoordinator *persistentStoreCoordinator;


@property (nonatomic, readonly) NSManagedObjectModel *managedObjectModel2;
@property (nonatomic, readonly) NSManagedObjectContext *managedObjectContext2;
@property (nonatomic, readonly) NSPersistentStoreCoordinator *persistentStoreCoordinator2;
- (NSString *)applicationDocumentsDirectory;

- (NSArray *)getAllCourses;

@end