CoreData 总结

#pragma mark - Core Data stack

//_managedObjectContext  管理上下文对象  可以进行增删改查(context),context 是一个全局属性(离不开它)

@synthesize managedObjectContext = _managedObjectContext;
//_managedObjectModel 管理对象模型  将工程里 的所有实体模型文件合并成一个管理对象模型 (实质:为了以后方便生成数据库中的表)

@synthesize managedObjectModel = _managedObjectModel;
//_persistentStoreCoordinator 持久化存储协调器(厨师,真正起作用的东西)(实际操作由它来完成)(java里数据持久化的那层)

@synthesize persistentStoreCoordinator = _persistentStoreCoordinator;

//NSPersistentStroe 持久化存储对象

//NSManageObject 管理对象(所谓的 model类,如student..)

//存储路径 Url格式(与split不同 为NSString格式)

- (NSURL *)applicationDocumentsDirectory {

    // The directory the application uses to store the Core Data store file. This code uses a directory named "com.zhangru.CoreDataDemo" in the application's documents directory.

    return [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];

}

#pragma mark--- 获取管理对象模型

- (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:@"Model" withExtension:@"momd"];

    _managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];

    return _managedObjectModel;
}

#pragma mark---获取持久化存储协调器

- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {

    // The persistent store coordinator for the application. This implementation creates and return 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:@"CoreDataDemo.sqlite"];

    NSError *error = nil;

    NSString *failureReason = @"There was an error creating or loading the application's saved data.";

    

    //NSMigratePersistentStoresAutomaticallyOption 设为YES 支持版本迁移

    //NSInferMappingModelAutomaticallyOption版本迁移映射

    if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:@{NSMigratePersistentStoresAutomaticallyOption:@YES,NSInferMappingModelAutomaticallyOption:@YES} 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();

    }

    NSLog(@"%@",storeURL);

    

    return _persistentStoreCoordinator;

}

#pragma mark---获取管理对象上下文

- (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] init];

    [_managedObjectContext setPersistentStoreCoordinator:coordinator];

    return _managedObjectContext;

}

//保存
#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();

        }

    }

}