I have a cloud function which attempts to add a "follower" to a users followers collection which will store this data:

id username timestamp

The username property isn't available so I need to get the user doc from firestore and store the username property value so I can add it when I create the new document in the users->following collection.

I've tried several different ways of getting the document but no matter what I try, I keep bumping into some promise related errors.

The current iteration of my function looks like this:

exports.onFollowCreate = functions.firestore
    .document('users/{user_id}/{following}/{id}')
    .onCreate((snap, context) => {
      const newValue = snap.data();
      const db = admin.firestore();
      db.collection("users")
          .doc(context.params.user_id)
          .update({followingCount: admin.firestore.FieldValue.increment(1)})
          .catch((er) => {
            console.log(er);
          });

      const userDocRef = admin.firestore().collection("users").doc(context.params.id);
      userDocRef.get().then((snapshot) => {
        if (snapshot.docs.length > 0) {
          snapshot.docs.foreach((doc) => {
            const username = doc.data();

            db.collection("users")
                .doc(newValue.id)
                .collection("followers")
                .doc(context.params.user_id)
                .set({
                  id: context.params.user_id,
                  username: username,
                  timeStamp: new Date(),
                })
                .catch((er) => console.log(er));
          });
        } else {
          console.log("Error: No documents found");
        }
      });
    });

Showing the following in the google cloud functions logs explorer:

Function execution started
Function returned undefined, expected Promise or value
Function execution took 3179 ms. Finished with status: ok
Exception from a finished function: TypeError: Cannot read properties of undefined (reading 'length')

CodePudding user response：

The reason you got error is because in the line:

 const userDocRef = admin.firestore().collection("users").doc(context.params.id);

The userDocRef will get exactly one doc. Instead of reaching it in the docs, you should check the document existence by snapshot.exists(). The docs field doesn't exist here, so snapshot.docs.length is throwing an error.

Besides of that, the code has multiple places to change:

1. Despite we don't need to use foreach at all, you don't need to wrap a pure foreach loop in a if statement.
2. If my understanding is right, the username is a string, but you will get a json file from snapshot.data(). Consider change the code to const username = doc.data()["username"];