Firebase数据库按键值查询

I have JSON like this.

我有这样的JSON。

   livefeeds= {
        "-KTn8pbqFHBUvgJ1Gwyl" =     {
            category = Alerts;
            text = "Samsung Galaxy Note 7 owners told to turn off device";
            timestamp = 1476179485648;
            "user_id" = V7EFBV6uATf8urLXX9eK4EHhxmG2;
        };
        "-KTn8pbrhHyNzeLh2vOq" =     {
            category = News;
            text = "Chicago Teachers Union, school board reach tentative contract agreement";
            timestamp = 1476179485648;
            "user_id" = V7EFBV6uATf8urLXX9eK4EHhxmG2;
        };
    }
   livef