javascript - Firestore - Listen to specific field change?

Question

How can I listen to a specific field change with firestore js sdk ?

In the documentation, they only seem to show how to listen for the whole document, if any of the "SF" field changes, it will trigger the callback.

db.collection("cities").doc("SF")
.onSnapshot(function(doc) {
    console.log("Current data: ", doc && doc.data());
});

question from:https://stackoverflow.com/questions/47860531/firestore-listen-to-specific-field-change

Answer 1

You can't. All operations in Firestore are on an entire document.

This is also true for Cloud Functions Firestore triggers (you can only receive an entire document that's changed in some way).

If you need to narrow the scope of some data to retrieve from a document, place that in a document within a subcollection, and query for that document individually.