数据库操作iOS库MagicalRecord使用说明（2）

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CoreData的使用（IOS学习）

——杂言：最近开始学习IOS7的开发，下文是在已经建好的项目里加入CoreData的结构，并实现一个基于coredata的简单save,query。

1. 引入Core Data Framework。选中项目-->Genaral-->Linked Frameworks and Libraries中添加“CoreData.Framework”。然后在prefix.pch中加入“#import<CoreData/CoreData.h>”

2. 加入数据模型，创建Model.xcdatamodeld文件。File-->New-->File-->IOS-->Core Data-->Data Model

3. 在Delegate中建立CoreData与Delegate的关联。点击XYZAppDelegate.h，在@interface与@end之中加入以下代码

1 @property (readonly, strong, nonatomic) NSManagedObjectContext *managedObjectContext;2 @property (readonly, strong, nonatomic) NSManagedObjectModel *managedObjectModel;3 @property (readonly, strong, nonatomic) NSPersistentStoreCoordinator *persistentStoreCoordinator;4 5 - (void) saveContext;6 - (NSURL *) applicationDocumentsDirectory;

4. 之后在XYZAppDelegate.m的@implementation下面写入以下代码（注：标红的2处名字请与.xcdatamodeld文件名保持一致）

1 @synthesize managedObjectContext = _managedObjectContext;2 @synthesize managedObjectModel = _managedObjectModel;3 @synthesize persistentStoreCoordinator = _persistentStoreCoordinator;

 1 - (void) saveContext 2 { 3     NSError *error = nil; 4      5     NSManagedObjectContext *managedObjectContext = self.managedObjectContext; 6     if(managedObjectContext != nil){ 7         if ([managedObjectContext hasChanges] && ![managedObjectContext save:&error]) { 8             NSLog(@"Unresolved error%@, %@", error, [error userInfo]); 9         }10     }11 }12 - (NSManagedObjectContext *) managedObjectContext13 {14     if (_managedObjectContext != nil) {15         return _managedObjectContext;16     }17     NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];18     if(coordinator != nil){19         NSLog(@"coordinator is not null-----");20         _managedObjectContext = [[NSManagedObjectContext alloc]init];21         [_managedObjectContext setPersistentStoreCoordinator:coordinator];22     }else{23         NSLog(@"coordinator is null-----");24     }25     return _managedObjectContext;26 }27 - (NSManagedObjectModel *) managedObjectModel28 {29     if(_managedObjectModel != nil){30         return _managedObjectModel;31     }32     NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"Ratings" withExtension:@"momd"];33     _managedObjectModel = [[NSManagedObjectModel alloc]initWithContentsOfURL:modelURL];34     return _managedObjectModel;35 }36 - (NSPersistentStoreCoordinator *) persistentStoreCoordinator37 {38     if(_persistentStoreCoordinator != nil){39         return _persistentStoreCoordinator;40     }41     NSURL *storeUrl = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"Ratings.sqlite"];42     NSError *error = nil;43     NSLog(@"storeUrl: %@",[self applicationDocumentsDirectory]);44     _persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc]initWithManagedObjectModel:[self managedObjectModel]];45     if(![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeUrl options:nil error:&error]){46         NSLog(@"Unresolved error %@%@", error, [error userInfo]);47         abort();48     }49     return _persistentStoreCoordinator;50 }51 - (NSURL *) applicationDocumentsDirectory52 {53     return [[[NSFileManager defaultManager]URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask]lastObject];54 }

5. 至此，Core Data的准备工作已经完毕。

6. 现在可以创建Entity并结合使用，打开Ratings.xcdatamodeld文件，面板如下(2种模式)，可以点击并添加Entity(可以结合右侧属性面板使用)

7. 为entity添加.m和.h文件，File-->New->File->IOS->Core Data->NSManagedObject subclass

8. entity已经创建完成，可以开始在Controller中使用相关context操作。我的是XYZPlayersViewController。

9. XYZPlayersViewController.h中添加以下代码

1 @property (nonatomic, strong) NSManagedObjectContext *context;

10. XYZPlayersViewController.m中需要使用的地方添加以下代码

1 @synthesize context;

 1 XYZAppDelegate *delegate = (XYZAppDelegate *)[[UIApplication sharedApplication]delegate]; 2 self.context = delegate.managedObjectContext; 3  4 Player *player = [NSEntityDescription insertNewObjectForEntityForName:@"Player" 5                                                inManagedObjectContext:context]; 6 player.name = @"timelyxyz"; 7 player.game = @"Chess"; 8 player.rating = [NSNumber numberWithInt:100]; 9 10 NSError *error = nil;11 if(![context save:&error]){12     NSLog(@"%@", [error localizedDescription]);13 }14 15 NSFetchRequest *fetchRequest = [[NSFetchRequest alloc]init];16 NSEntityDescription *entity = [NSEntityDescription entityForName:@"Player"17                                           inManagedObjectContext:context];18 [fetchRequest setEntity:entity];19 20 NSArray *fetchObjects = [context executeFetchRequest:fetchRequest error:&error];21 for(NSManagedObject *info in fetchObjects){22     NSLog(@"name: %@",[info valueForKey:@"name"]);23     NSLog(@"game: %@", [info valueForKey:@"game"]);24     NSLog(@"rating: %@", [info valueForKey:@"rating"]);25 }

11. log输出如下

demo下载：Ratings

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