Firebase functions: getting document data inside a function-CodePudding

im making a type of chat app. Im trying to write a firestore function that listens to a specific document that, when updated, will trigger the function to send a push notification to a specific user. However, im receiving an error. So far, i have:

export const messageListener = functions.firestore
    .document("stingrayMessageListener/stingrayMessageListener")
    .onWrite(async (change) => {
      const beforeData = change?.before?.data();
      const afterData = change?.before?.data();
      if (beforeData?.receiverId!=afterData?.receiverId) {
        const docRef = admin.firestore().doc("users/${afterData?.receiverId}");
        const docSnap = await docRef.get();
        const payload = {
          notification: {
            title: "New message!",
            body: "${afterData?.senderName} has sent you a message!",
          },
          data: {
            body: "message",
          },
        };
        admin.messaging().sendToDevice(docSnap.data()?.token, payload);
      }
    });

This function is spitting out the following error:

Registration token(s) provided to sendToDevice() must be a non-empty string or a non-empty array

Im pretty sure this is implying that docSnap() is returning as null, because token is a field on all user documents. Am I doing something wrong?

CodePudding user response：

So, turns out it was a very simple solution. In Typescript, you can dont use "" to use a variable in a string. You use ``.

CodePudding user response：

In addition to using template literals in your document paths as you answered, both beforeData and afterData are assigned to change?.before?.data(), meaning your function won't send notifications to any device:

const beforeData = change?.before?.data();
const afterData = change?.before?.data();
if (beforeData?.receiverId != afterData?.receiverId) {
    //above condition won't be true
...

You'd only need to use the after property holding the changed document.

const afterData = change?.after?.data();

Let me know if this was helpful.