Firebase Firestore DocumentReference in Typescript is not returning the document properties

I’m writing a Firebase Cloud Function that will write a Firestore document and then return the documents unique ID to a Flutter app. I’m using Typescript to write my functions.

This is the code that writes the document:

db.collection('devices').doc().set({"deviceId": userId},{merge: true})
    .then((docRef: FirebaseFirestore.DocumentReference<FirebaseFirestore.DocumentData>) => {
        functions.logger.info(`Document path: ${docRef.path}`,{structuredData: true});
        functions.logger.info(`Document written with ID: ${docRef.id}`,{structuredData: true});
        response.status(200).send({"result":"success", "docId": docRef.id});
    })
    .catch((error: Error) => {
        functions.logger.error(error,{structuredData: true});
        response.status(200).send({"result":"error", "message": error.message});
    });

The set method returns a promise with a payload that should be of the type DocumentReference and contain the id.
The document is being written to Firestore, but it is not getting the values of the DocumentReference so I can send it back in the response.

>Solution :

The set() method returns a WriteResult object that only has a writeTime property. It’s add() method that returns a DocumentReference so try using that instead as shown below:

db.collection("devices").add({ deviceId: userId })
  .then((docRef) => {
    functions.logger.info(`Document written with ID: ${docRef.id}`,{structuredData: true});
  })

If you want to use set() then you’ll have to store the document ID before itself like this:

const newDocRef = db.collection("devices").doc();

newDocRef.set({ deviceId: userId })
  .then(() => {
    functions.logger.info(`Document written with ID: ${newDocRef.id}`,{structuredData: true});
  })

Either ways, you don’t need {merge: true} as they’ll create a new document.