Firestore user id is different of the document id react native firebase

Question

I'm doing a simple user creation, but the id field in the firestore is null and the ids are different.

why is this happening? how to solve?

code below:

const auth = await authFB().createUserWithEmailAndPassword(data.email, data.password);

const db = firestore();

await db
        .collection('Clients')
        .doc(auth.user.uid)
        .set({
          id: auth.user.uid,
          name: {
            first: firstName,
            last: lastName
            }
         });

Document image below: (Look at id: null):

Answer 1

The solution is to create const uid = auth.user.uid and use this constant in two paces inside firestore update. For example:

const auth = await authFB().createUserWithEmailAndPassword(data.email, data.password);

const uid = auth.user.uid;      // <----

const db = firestore();

await db
        .collection('Clients')
        .doc(uid)              // <----
        .set({
          id: uid,             // <----
          name: {
            first: firstName,
            last: lastName
            }
         });