关于Core Data的一些整理（一）

关于Core Data的一些整理（一）

在Xcode7.2中只有Mast-Debug和Single View中可以勾选Use Core Data

如果勾选了Use Core Data，Xcode会自动在AppDelegate中帮你生成Core Data的核心代码，并且自动生成.xcdatamodeld数据文件

 

//Appdelegate.h中
#import <UIKit/UIKit.h>
#import <CoreData/CoreData.h>

@interface AppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) UIWindow *window;

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

- (void)saveContext;
- (NSURL *)applicationDocumentsDirectory;


@end



//Appdelegate.m中系统帮助生成的代码
- (void)applicationWillTerminate:(UIApplication *)application {
  // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
  // Saves changes in the application's managed object context before the application terminates.
  [self saveContext];
}

#pragma mark - Core Data stack

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

- (NSURL *)applicationDocumentsDirectory {
    // The directory the application uses to store the Core Data store file. This code uses a directory named "qq100858433.JMHitList" in the application's documents directory.
    return [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
}

- (NSManagedObjectModel *)managedObjectModel {
    // The managed object model for the application. It is a fatal error for the application not to be able to find and load its model.
    if (_managedObjectModel != nil) {
        return _managedObjectModel;
    }
    NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"JMHitList" withExtension:@"momd"];
    _managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
    return _managedObjectModel;
}

- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {
    // The persistent store coordinator for the application. This implementation creates and returns a coordinator, having added the store for the application to it.
    if (_persistentStoreCoordinator != nil) {
        return _persistentStoreCoordinator;
    }
    
    // Create the coordinator and store
    
    _persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
    NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"JMHitList.sqlite"];
    NSError *error = nil;
    NSString *failureReason = @"There was an error creating or loading the application's saved data.";
    if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) {
        // Report any error we got.
        NSMutableDictionary *dict = [NSMutableDictionary dictionary];
        dict[NSLocalizedDescriptionKey] = @"Failed to initialize the application's saved data";
        dict[NSLocalizedFailureReasonErrorKey] = failureReason;
        dict[NSUnderlyingErrorKey] = error;
        error = [NSError errorWithDomain:@"YOUR_ERROR_DOMAIN" code:9999 userInfo:dict];
        // Replace this with code to handle the error appropriately.
        // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }
    
    return _persistentStoreCoordinator;
}


- (NSManagedObjectContext *)managedObjectContext {
    // Returns the managed object context for the application (which is already bound to the persistent store coordinator for the application.)
    if (_managedObjectContext != nil) {
        return _managedObjectContext;
    }
    
    NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
    if (!coordinator) {
        return nil;
    }
    _managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
    [_managedObjectContext setPersistentStoreCoordinator:coordinator];
    return _managedObjectContext;
}

#pragma mark - Core Data Saving support

- (void)saveContext {
    NSManagedObjectContext *managedObjectContext = self.managedObjectContext;
    if (managedObjectContext != nil) {
        NSError *error = nil;
        if ([managedObjectContext hasChanges] && ![managedObjectContext save:&error]) {
            // Replace this implementation with code to handle the error appropriately.
            // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
            NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
            abort();
        }
    }
}

@end

假如你在.xcdatamodeld中生成了如下实体和实体属性：

 

那么在VC中获取数据库内容和添加数据库内容的代码如下：

  //从Core Data中获得已有数据
  id appDelegate = [UIApplication sharedApplication].delegate;
  NSManagedObjectContext *managedContext = [appDelegate managedObjectContext];
  NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Person"];
  @try {
    self.people = [NSMutableArray arrayWithArray:[managedContext executeFetchRequest:fetchRequest error:nil]];
  }
  @catch (NSException *exception) {
    NSLog(@"Could not fetch %@", [exception userInfo]);
  }
  @finally {
    NSLog(@"Fetch Successful");
  }
  
  //为数据库添加实体实例
  id appDelegate = [UIApplication sharedApplication].delegate;
  //NSManagedObjectContext可以看做内存中用来处理managedObjects的暂存器
  NSManagedObjectContext *mangedContext = [appDelegate managedObjectContext];
  //下面两种方法都可以获得Person实体
//  NSEntityDescription *entity = [NSEntityDescription entityForName:@"Person" inManagedObjectContext:mangedContext];
//  NSManagedObject *person = [[NSManagedObject alloc] initWithEntity:entity insertIntoManagedObjectContext:mangedContext];
//  [person setValue:name forKey:@"name"];
  NSManagedObject *person = [NSEntityDescription insertNewObjectForEntityForName:@"Person" inManagedObjectContext:mangedContext];
  [person setValue:name forKey:@"name"];
  @try {
    [mangedContext save:nil];
    [self.people addObject:person];
  }
  @catch (NSException *exception) {
    NSLog(@"Could not save %@", [exception userInfo]);
  }
  @finally {
    NSLog(@"Save Successfullt!");
  }