JavaScript 中的非法返回语句

Question

不会删除具有 1 个以上子节点的“天”节点。我该如何解决这个问题？

我需要确保我的承诺冒泡到顶层的最后一个 then()。所以我需要在collectionRef.once 之前返回。但是该 return 语句现在阻止了 collectionRef.once 的发生。我被困住了！

这是我的代码

const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp(functions.config().firebase);
const defaultDatabase = admin.database();

exports.deleteOldItems = functions.database.ref('/path/to/items/{pushId}')
.onWrite(event => {
  var ref = event.data.ref.parent; // reference to the items
  var now = Date.now();
  var cutoff = now - 2 * 60 * 60 * 1000;
  var oldItemsQuery = ref.orderByChild('timestamp').endAt(cutoff);
  return oldItemsQuery.once('value', function(snapshot) {
    // create a map with all children that need to be removed
    var updates = {};
    snapshot.forEach(function(child) {
      updates[child.key] = null
    });
    // execute all updates in one go and return the result to end the function
    return ref.update(updates);
  }).then(function() {;

    const theRef = event.data.ref;
    const collectionRef = theRef.parent.child('days');
    return collectionRef; // ILEGAL RETURN STATEMENT
    collectionRef.once('value').then(messagesData => {
        if(messagesData.numChildren() > 1) {

  let updates = {};
updates['/days'] = null;
return defaultDatabase.ref().update(updates); // 'days' doesn't get removed even if it has more than 1 child (as in the image)!
        }
    })
});

});

数据结构：https://i.stack.imgur.com/gVn8S.jpg

Answer 1

exports.deleteOldItems = functions.database.ref('/path/to/items/{pushId}')
  .onWrite(event => {
    var ref = event.data.ref.parent // reference to the items
    var now = Date.now()
    var cutoff = now - 2 * 60 * 60 * 1000
    var oldItemsQuery = ref.orderByChild('timestamp').endAt(cutoff)
    return oldItemsQuery.once('value', function(snapshot) {
      // create a map with all children that need to be removed
      var updates = {}
      snapshot.forEach(function(child) {
        updates[child.key] = null
      })
      // execute all updates in one go and return the result to end the function
      return ref.update(updates)
    }).then(function() {
      // const theRef = event.data.ref
      const collectionRef = defaultDatabase.ref().child('/days')
      // return collectionRef // ILEGAL RETURN STATEMENT
      collectionRef.once('value').then(messagesData => {
                console.log(`Hello messageData : ${messagesData.numChildren()}`)
              if(messagesData.numChildren() > 1) {
                    const updates = {}
                    updates['/days'] = null
                    return defaultDatabase.ref().update(updates); // 'days' doesn't get removed even if it has more than 1 child (as in the image)!
                }
      })
  })

使用defaultDatabase.ref().child('/days') 而不是event.data.ref.parent

还请阅读文档并了解 Promise 的工作原理，它将对您的未来有所帮助。目前，这些更改将起作用。在我结束时进行了测试。

您必须观看的视频

What's the difference between event.data.ref and event.data.adminRef? - #AskFirebase Asynchronous Programming (I Promise!) with Cloud Functions for Firebase - Firecasts

您可以订阅他们的Firebase YouTube Channel 以获取最新更新并了解更多信息。