Question 226477 in Javascript Question posted in
A very good W3school tutorial can be found here.

Javascript – Firebase Firestore: How to know if setDoc created or overwrote a document

With latest version of Firebase Javascript SDK (10.1.0) I am using signInWithPopup to authenticate users through Providers and then saving their credentials inside the DB:

  userCredentials = await signInWithPopup(auth, new GoogleAuthProvider());
  await setDoc(
    doc(db, "users", userCredentials.user.uid),
    {
      uid: userCredentials.user.uid,
      email: userCredentials.user.email,
      ...,
    },
    { merge: true },
  );

How can I know if the recently set document was created (user was authenticated for the first time, i.e. signed up to the service) or updated (user was already registered)?

PS: I would like to avoid querying the DB to check for existing email, as I would need to change the access rules and make all users data available to anyone.

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2

Answers


  1. 0

    I normally used getDoc for such use cases. I call it before setDoc. Based on your example code I would adapt my code like this:

    const userDocRef = doc(db, "users", userCredentials.user.uid);
const userDocSnapshot = await getDoc(userDocRef);

if (userDocSnapshot.exists()) {
  // Document exists, so the user was already registered
  await updateDoc(userDocRef, {
    // fields to update
  });
} else {
  // Document does not exist, so the user is signing up for the first time
  await setDoc(userDocRef, {
    uid: userCredentials.user.uid,
    email: userCredentials.user.email,
    // other fields
  });
}

    Let me know if something is unclear or bad commented and everyone feel free to edit.

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  2. 0

    The only way to know if a Firestore document is present in the database is to query it.

    As a workaround you could use the updateDoc() method to write to the DB and in case the doc does not already exist it will return an error of type FirebaseError: No document to update and you would then use the setDoc() method in a catch() block to create it.

    BUT note that this approach costs a write each time the doc does not exist. It’s up to you to do the math to calculate the best option for you (pay for a read each time you want to know if the doc exists or pay for an extra write when you actually create the doc).

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