Angular Firestore document update causing infinite loop in subscription - firebase

Question

I understand the issue but can't figure out the workaround. I am querying a specific document to extract an array of token strings. I need to append a new token to the end of this string and then update the current document with this new token array.
To do this, I have subscribed to a query and within, I update that document. But of course, when you update the same object, the subscription runs again thus creating an infinite loop. I tried incorporating a take(1) pipe rxjs operator but that did not change anything. Any suggestions?
Here's my code:
this.afs.collection('users').doc(user.userUID).valueChanges().pipe(take(1)).subscribe((user: userModel) => {
const currentTokens: string[] = user.notifTokens ? user.notifTokens : [];
//token variable is provided outside this query
currentTokens.push(token);
//this next lines causes the subscription to trigger again
userRef.doc(user.userUID).update({notifTokens: currentTokens})
})

Answer 1

I would recommend you avoid using a subscription in this situation, for exactly this reason. I realize the Angularfire2 docs don't list this method, but the base Firebase package includes a .get() method... and while the AF2 docs don't mention the .get() method... the source code shows that it is supported.
Try something like:
this.afs.collection('users').doc(user.userUID).get().then( (user: userModel) => {
if (user.exists) {
console.log("Document data:", user.data());
// Do stuff with the info you get back here
const currentTokens: string[] = user.data().notifTokens ? user.data().notifTokens : [];
currentTokens.push(token);
userRef.doc(user.data().userUID).update({notifTokens: currentTokens})
} else {
// user.data() will be undefined in this case
console.log("No such document!");
}
}).catch(function(error) {
console.log("Error getting document:", error);
});