How to check if document exist on SET and WHERE

Question

I'm trying to update PITA denormalised db structure. I know there are already answers on how to check if document exist on get even documentation is pretty clear about it but I just cannot find anything what would check if document exist on update "set" and "where".

First I want to check one document if exist before updating

 const staffRef = db.collection("staff").doc(uid)

    return staffRef.set({
        employeeProfile: employeeProfile
    }, {
            merge: true
        })...

Is there any way to check if that document exist on set or should I first read it to find out if that document exist like this

    const staffRef = db.collection("staff").doc(uid)
    return staffRef.get()
        .then((doc) => {
            if (doc.exists) {
                return staffRef.set({
                    employeeProfile: employeeProfile
                }, {...

Second I want to check multiple documents on where

const staffRef = db.collection("staff").where("employerId", "==", uid)
    const batch = db.batch()

    return staffRef.get()
        .then((querySnapshot) => {
            querySnapshot.forEach((doc) => {
                batch.update(doc.ref, { employerProfile: employerProfile })
            })...

Should I read the each doc after forEach if exist?

Answer 1

First answer: Yes, for a single document, you have to first use the get() method to find out if that document exists.

For a DocumentSnapshot that points to a non-existing document, any data access will return 'undefined'. You can use the exists property to explicitly verify a document's existence.

Second answer: No, in case of the results of a Query , you don't need to check each document: each doc you get by looping with querySnapshot.forEach() does exist.

A QuerySnapshot contains zero or more DocumentSnapshot objects representing the results of a query.