How to get the auto generated ID of a Firestore document?

Question

I use the auto generated ID when I create my document. After setting, I need to get it.

await admin.firestore().collection("mycollection").doc().set(mydata)  
    .then(doc => {

        console.log(doc.id);

        return true;
     })
     .catch(err => {
         return false;
     });

The retrieved ID in the log is not the same as the ID in the Firestore Database. I don't understand why.

Answer 1

The retrieved ID in the log is not the same as the ID in the Firestore Database.

This is normal, since the set() method returns a Promise<void> (ie a Promise which resolves to an undefined ). Therefore you cannot do doc.id in the callback function passed to the then() method, since doc is undefined .

You should do as follows:

try {
  const docRef = admin.firestore().collection("mycollection").doc();
  const docId = docRef.id;  //Here you have the value of the id (independently of the fact you call set() later or not)

  await docRef.set(mydata);
} catch(err) {
  //...
}