incrementKey 方法服务器数据和本地数据不一致

下面这段代码，执行完成后打印a的count是2，但是数据库里面a的count是1

 AVObject* a = [AVObject objectWithClassName:@"A"];
    [a saveInBackgroundWithBlock:^(BOOL succeeded, NSError *error) {
        if(succeeded)
        {
            [a incrementKey:@"count"];
            
            AVObject* b = [AVObject objectWithClassName:@"B"];
            b[@"a"] = a;
            [b saveInBackgroundWithBlock:^(BOOL succeeded, NSError *error) {
                if(succeeded)
                {
                    [a incrementKey:@"count"];
                    [b saveInBackgroundWithBlock:^(BOOL succeeded, NSError *error) {
                        if(succeeded)
                        {
                            NSLog(@"%@", a);
                        }
                    }];
                }
            }];
        }
    }];