如何通过云触发 Firestore 收集 function

Question

I want to trigger a new collection (timeline collection) from the existing collection of followers collection and videos collection whenever I clicked the following button in my app.

Now the problem is that, the Cloud Function is created from the view log but the new collection (timeline collection) won't be created.

Below is the code for the Cloud Function where I target the followers collection and the videos collection to create a new timeline collection. I anticipate for your help.

• Videos collection

• Followers collection

• Cloud function view logs

const functions = require("firebase-functions");
    const admin = require("firebase-admin");
    admin.initializeApp();
    
    // // Create and Deploy Your First Cloud Functions
    // // https://firebase.google.com/docs/functions/write-firebase-functions
    //
    // exports.helloWorld = functions.https.onRequest((request, response) => {
    //  response.send("Hello from Firebase!");
    // });
    exports.onCreateFollower = functions.firestore
      .document("/followers/{userId}/userFollowers/{userfollowerId}")
      .onCreate(async (snapshot, context) => {
        console.log("The Event has Created The Follower", snapshot.id);
        const userId = context.params.userId;
        const userfollowerId = context.params.userfollowerId;
    
        // 1) Create followed users posts ref
        const followedUserVideosCollection = admin
          .firestore()
          .collection("videos")
          .doc(userId)
          .collection("userVideos"); 
    
        // 2) Create following user's timeline ref
        const timelineVideosCollection = admin
          .firestore()
          .collection("timeline")
          .doc(userfollowerId)
          .collection("timelinePosts");
    
        // 3) Get followed users posts
        const querySnapshot = await followedUserVideosCollection.get();
    
        // 4) Add each user post to following user's timeline
        querySnapshot.forEach(doc => {
          if (doc.exists) {
            const videoId = doc.id;
            const videoData = doc.data();
            timelineVideosCollection.doc(videoId).set(videoData);
          }
        });
      });

Answer 1

I figured out what causes the error "querySnapshot.forEach isn't a function". According to this answer , you need to query the collection first because get() returns a document instead of a snapshot. Here's a sample code (see step 3):

// 1) Create followed users posts ref
const followedUserVideosCollection = admin
    .firestore()
    .collection("videos")
    .doc("Videos 1") // I changed the value with your sample for test purposes and also because I'm not sure how you fill up this doc.
    .collection("userVideos");

// 2) Create following user's timeline ref
const timelineVideosCollection = admin
    .firestore()
    .collection("timeline")
    .doc(userfollowerId)
    .collection("timelinePosts");

// 3) Get followed users posts & Add each user post to following user's timeline
await followedUserVideosCollection.where('id', '==', 0).get().then((querySnapshot) => {
    if (querySnapshot) {
        querySnapshot.forEach(doc => {
            if (doc) {
                const videoId = doc.id;
                const videoData = doc.data();
                timelineVideosCollection.doc(videoId).set(videoData);
            }
        });
    }else {
        console.log("Document not found");
    }
}).catch((error) => {
    console.log(error);
});

A solution is to create a filter, and make sure that the document you're looking for matches the filter. For example, a document inside the subcollection userVideos should have a field called id with value of 0.

You may have to remodel your DB to fix the line where I put a comment but this code should write the timeline collection.