在将值设置为state之前对fire base snapshot进行排序

Question

我从fire-base获得了值，因为fire-base不支持组合多个orderByChild()，我想我们必须在客户端对值进行排序

fire-base查询是

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: {} });
    }
}

火力响应

{ 
   "-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"
   }
}

我想通过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这样的代码片段：

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

看到这个可运行的版本：

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);

有几点需要注意：

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。见http://stackoverflow.com/questions/26700924/query-based-on-multiple-where-clauses-in-firebase。
2. 当您调用snapshot.val()时，您将抛出Firebase为数据返回的订单信息。我不认为这是一个问题，但如果你想保持这种排序，使用snapshot.forEach()循环结果。见orderByChild not working in Firebase。
3. 您的日期格式在最后一个孩子中似乎有缺陷："createdAt":"2017-11-28 18:55:1"。这应该是"createdAt":"2017-11-28 18:55:01"，以使其可靠地排序。