javascript - 在将值设置为 state 之前对 Firebase 快照进行排序

Question

我从 Firebase 获取值，因为 Firebase 不支持组合多个 orderByChild()，我想我们必须在客户端对值进行排序

Firebase 查询为

componentDidMount() {
    const device_id = DeviceInfo.getUniqueID();
    this.codesRef = firebase.database().ref(`codes`).orderByChild('owner').equalTo(device_id);
    this.codesRef.keepSynced(true);
    this.codesRef.on('value', this.handleCodesUpdate);
}

componentWillUnmount() {
    this.codesRef.off('value', this.handleCodesUpdate);
}

handleCodesUpdate(snapshot) {
    if (snapshot.val()) {

        //sort the snapshot before assigning to state

        this.setState({ codes: snapshot.val() });
    }
    else {
        this.setState({ codes: {} });
    }
}

Firebase 响应

{ 
   "-L1SI6Ceu2mPCxDU89NH":{  
      "status":0,
      "purchase_date":1514467520472,
      "title":"Mnic Htod",
      "start_in":0,
      "owner":"fgdgfdgdfgdfgdfgdfg",
      "valid_duration":1,
      "createdAt":"2017-11-28 18:55:20",
      "code":"218688"
   },
   "-L1SI3krvOYDaqr8g_cs":{  
      "status":0,
      "purchase_date":1514467510437,
      "title":"Banfog",
      "start_in":0,
      "owner":"xgdfgdfgdfgfdgdf",
      "valid_duration":1,
      "createdAt":"2017-11-28 18:55:10",
      "code":"804452"
   },
   "-L1SI1eFHX7a0_RFhZtW":{  
      "status":0,
      "purchase_date":1514467501822,
      "title":"Blizaard",
      "start_in":0,
      "owner":"xcvxcvxcvxcvxcv",
      "valid_duration":1,
      "createdAt":"2017-11-28 18:55:1",
      "code":"300149"
   }
}

我想按createdAt对数据进行排序

期待急需的帮助

谢谢

Answer 1

最简单的方法是使用如下代码片段:

var sortedKeys = Object.keys(json).sort(function(a,b) { 
  return json[b].createdAt < json[a].createdAt 
});

查看这个可运行版本:

var json = { 
   "-L1SI6Ceu2mPCxDU89NH":{  
      "status":0,
      "purchase_date":1514467520472,
      "title":"Mnic Htod",
      "start_in":0,
      "owner":"fgdgfdgdfgdfgdfgdfg",
      "valid_duration":1,
      "createdAt":"2017-11-28 18:55:20",
      "code":"218688"
   },
   "-L1SI3krvOYDaqr8g_cs":{  
      "status":0,
      "purchase_date":1514467510437,
      "title":"Banfog",
      "start_in":0,
      "owner":"xgdfgdfgdfgfdgdf",
      "valid_duration":1,
      "createdAt":"2017-11-28 18:55:10",
      "code":"804452"
   },
   "-L1SI1eFHX7a0_RFhZtW":{  
      "status":0,
      "purchase_date":1514467501822,
      "title":"Blizaard",
      "start_in":0,
      "owner":"xcvxcvxcvxcvxcv",
      "valid_duration":1,
      "createdAt":"2017-11-28 18:55:1",
      "code":"300149"
   }
}
var sortedKeys = Object.keys(json).sort(function(a,b) { return json[b].createdAt < json[a].createdAt });
console.log(sortedKeys);

需要注意的几点:

1. 您无法让 Firebase 在服务器端执行此操作，因为它只能对单个属性进行排序/过滤。请参阅http://stackoverflow.com/questions/26700924/query-based-on-multiple-where-clauses-in-firebase .
2. 当您调用 snapshot.val() 时，您将丢弃 Firebase 为数据返回的订单信息。我认为这不是问题，但如果您想保持该顺序，请使用 snapshot.forEach() 循环结果。请参阅orderByChild not working in Firebase .
3. 您的日期格式在最后一个子项中似乎有缺陷:"createdAt":"2017-11-28 18:55:1"。应该是 "createdAt":"2017-11-28 18:55:01" 以使其可靠地排序。