javascript - 对 Firebase 数据库中的数据集取平均值

Question

我正在设计一个应用程序，但对 Javascript 有点不适应。到目前为止，我有一个具有以下结构的 Firebase 实时数据库。[!

我想做的是每次添加/更新绿色区域时，从该绿色区域中获取一个值(红色)，从每个绿色对象中保存的所有值中获取平均值并放置它变成底部的棕色物体。

有人知道如何使用 Javascript/Firebase 函数完成此操作吗？

JSON 导出:

{
  "5Rz8DpU34PeXAcnriD6vEiPu7jk2" : {
    "UiWK7RkdeCbUte8g7naB9qp42qu1" : {
      "rating1" : 5
    },
    "average" : 0
  },
  "Fi43uP2LcbVLi2uFwUyCAp2uvSH2" : {
    "average" : 0
  },
  "UiWK7RkdeCbUte8g7naB9qp42qu1" : {
    "Fi43uP2LcbVLi2uFwUyCAp2uvSH2" : {
      "rating1" : 5,
      "rating2" : 5
    },
    "asdas" : {
      "rating1" : 2
    },
    "average" : 0
  },
  "gov4hRpDgDVhyVgsQrYJnn1rfeW2" : {
    "UiWK7RkdeCbUte8g7naB9qp42qu1" : {
      "rating1" : 5
    },
    "average" : 0
  }
}

Answer 1

以下 Cloud Function 代码应该可以解决问题:

const admin = require('firebase-admin');
admin.initializeApp();
const db = admin.database();

exports.average = functions.database
  .ref('/ratings/{blueId}/{greenId}')
  .onWrite((change, context) => {
    const blueId = context.params.blueId;
    const blueRef = db.ref('ratings/' + blueId);

    const blueAverageRef = db.ref('ratings/' + blueId + '/average');

    let totalSum = 0;
    let nbrOfElem = 0;

    return blueRef
      .once('value', function(snapshot) {
        snapshot.forEach(function(childSnapshot) {
          if (childSnapshot.val().val) {
            //console.log(childSnapshot.val());
            totalSum += childSnapshot.val().val;
            nbrOfElem++;
          }
        });
      })
      .then(() => {
        //console.log('totalSum: ' + totalSum);
        //console.log('nbrOfElem: ' + nbrOfElem);
        return blueAverageRef.transaction(function(average) {
          if (nbrOfElem > 0) {
            return { val: totalSum / nbrOfElem };
          } else {
            return 0;
          }
        });
      })
      .catch(error => {
        console.log(error);
      });
  });

请注意，它使用了一个事务，请参阅 https://firebase.google.com/docs/database/web/read-and-write#save_data_as_transactions和 https://firebase.google.com/docs/reference/js/firebase.database.Reference#transaction

数据库的结构应为:

-ratings
   -blueNode1
      -greenNode11
         -val:2  // <- red node in your picture
      -greenNode12
         -val:10
      -average   // <- red node in your picture
         -val:6
   -blueNode2
      -greenNode21
         -val:5
      -greenNode22
         -val:3
      -greenNode23
         -val:1
      -average
         -val:5