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: 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!");
   }