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:100];

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