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

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

 - (void) saveContext;
 - (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）

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

 - (void) saveContext
 {
     NSError *error = nil;

     NSManagedObjectContext *managedObjectContext = self.managedObjectContext;
     if(managedObjectContext != nil){
         if ([managedObjectContext hasChanges] && ![managedObjectContext save:&error]) {
             NSLog(@"Unresolved error%@, %@", error, [error userInfo]);
         }
     }
 }
 - (NSManagedObjectContext *) managedObjectContext
 {
     if (_managedObjectContext != nil) {
         return _managedObjectContext;
     }
     NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
     if(coordinator != nil){
         NSLog(@"coordinator is not null-----");
         _managedObjectContext = [[NSManagedObjectContext alloc]init];
         [_managedObjectContext setPersistentStoreCoordinator:coordinator];
     }else{
         NSLog(@"coordinator is null-----");
     }
     return _managedObjectContext;
 }
 - (NSManagedObjectModel *) managedObjectModel
 {
     if(_managedObjectModel != nil){
         return _managedObjectModel;
     }
     NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"Ratings" withExtension:@"momd"];
     _managedObjectModel = [[NSManagedObjectModel alloc]initWithContentsOfURL:modelURL];
     return _managedObjectModel;
 }
 - (NSPersistentStoreCoordinator *) persistentStoreCoordinator
 {
     if(_persistentStoreCoordinator != nil){
         return _persistentStoreCoordinator;
     }
     NSURL *storeUrl = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"Ratings.sqlite"];
     NSError *error = nil;
     NSLog(@"storeUrl: %@",[self applicationDocumentsDirectory]);
     _persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc]initWithManagedObjectModel:[self managedObjectModel]];
     if(![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeUrl options:nil error:&error]){
         NSLog(@"Unresolved error %@%@", error, [error userInfo]);
         abort();
     }
     return _persistentStoreCoordinator;
 }
 - (NSURL *) applicationDocumentsDirectory
 {
     return [[[NSFileManager defaultManager]URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask]lastObject];
 }

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

 @property (nonatomic, strong) NSManagedObjectContext *context;

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

 @synthesize context;

 XYZAppDelegate *delegate = (XYZAppDelegate *)[[UIApplication sharedApplication]delegate];
 self.context = delegate.managedObjectContext;

 Player *player = [NSEntityDescription insertNewObjectForEntityForName:@"Player"
                                                inManagedObjectContext:context];
 player.name = @"timelyxyz";
 player.game = @"Chess";
 player.rating = [NSNumber numberWithInt:];

 NSError *error = nil;
 if(![context save:&error]){
     NSLog(@"%@", [error localizedDescription]);
 }

 NSFetchRequest *fetchRequest = [[NSFetchRequest alloc]init];
 NSEntityDescription *entity = [NSEntityDescription entityForName:@"Player"
                                           inManagedObjectContext:context];
 [fetchRequest setEntity:entity];

 NSArray *fetchObjects = [context executeFetchRequest:fetchRequest error:&error];
 for(NSManagedObject *info in fetchObjects){
     NSLog(@"name: %@",[info valueForKey:@"name"]);
     NSLog(@"game: %@", [info valueForKey:@"game"]);
     NSLog(@"rating: %@", [info valueForKey:@"rating"]);
 }

11. log输出如下

demo下载：Ratings