coredata 最简单例子

先按照网上的教程，建一个简单的带coredata的项目
再 添加一个 UserInfo 对象（表）（按照网上的教材，可视化方式添加）

然后在AppDelegate.m中按如下修改，（只添加了4个方法）

然后运行，看控制台日志


- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    // Override point for customization after application launch.
    self.window.backgroundColor = [UIColor whiteColor];
    [self.window makeKeyAndVisible];
        
    [self addUser];       
    [self gainDatas];
    
    return YES;
}
//添加
-(void)addUser{
    UserInfo * userInfo  = [NSEntityDescription insertNewObjectForEntityForName:@"UserInfo" 
                                                         inManagedObjectContext:self.managedObjectContext];    
    userInfo.name = @"dage";
    userInfo.password = @"password3";
    NSError *error = nil;
    if (![self.managedObjectContext save:&error]) {        
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }
    
    NSLog(@"add success");
    
}
//查询
-(void)gainDatas {    
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    [fetchRequest setEntity:[NSEntityDescription entityForName:@"UserInfo" inManagedObjectContext:self.managedObjectContext]];
    
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"name like[cd]'baobao'"];//查询条件
    // NSPredicate *predicate = [NSPredicate predicateWithFormat:@"password='password3'"];//查询条件
    
    NSMutableArray *sortDescriptors = [NSMutableArray array];    //排序用
    [sortDescriptors addObject:[[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES] ];  //排序用
    
    [fetchRequest setPredicate:predicate];  //查询条件
    [fetchRequest setFetchBatchSize:5];     //分页  
    [fetchRequest setSortDescriptors:sortDescriptors];  //排序
    [fetchRequest setReturnsObjectsAsFaults:NO];
    [fetchRequest setPropertiesToFetch:[NSArray arrayWithObjects:@"name", @"password", nil]];  //查询的字段，一般不需要
    NSError *error = nil;
    NSArray *fetchedItems = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];
    if (fetchedItems == nil) {
        NSLog(@"fetch request resulted in an error %@, %@", error, [error userInfo]);
    }else {
        NSLog(@"fetchedItems=%d",fetchedItems.count);
        for (UserInfo *user in fetchedItems) {
            NSLog(@"user.authour=%@",user.name);
            // [self deleteUser:user];  //删除            
            // [self updateUser:user];  //更新
        }
    }    
}
//删除：NSManagedObject对象必须先取出来，用managedObjectContext删除，保存就好
-(void)deleteUser:(id)user{
    [self.managedObjectContext deleteObject:user];  
    NSError *error = nil;
    if (![self.managedObjectContext save:&error]) {        
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }
    
    NSLog(@"delete success");    
}
//更新：直接修改对象，保存managedObjectContext就好
-(void)updateUser:(UserInfo*)user{
    user.name = @"baobao";   //修改后，直接保存managedObjectContext就可以了 
    NSError *error = nil;
    if (![self.managedObjectContext save:&error]) {        
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }
    
    NSLog(@"update success");    
}