Can a firestore snapshot contain x number of changed documents

Question

I want to ask about Firestore

Reading the docs

When a document is added, removed or modified then I get a signal about that event here in this code from the doc:

db.collection("cities").where("state", "==", "CA")
    .onSnapshot((snapshot) => {
        snapshot.docChanges().forEach((change) => {
            if (change.type === "added") {
                console.log("New city: ", change.doc.data());
            }
            if (change.type === "modified") {
                console.log("Modified city: ", change.doc.data());
            }
            if (change.type === "removed") {
                console.log("Removed city: ", change.doc.data());
            }
        });
    });

1. When I start this listener will I then get all document matching "state", "==", "CA" even if it's 100.000 of them? Will they come all at once or in batches?

2. after the above initial all (100.000) will I after that always get one(1) document, like when a doc is modified, added or removed, or can there be like a batch collapsing latency from firestore so I will get 1-to-many in the snapshot?

Answer 1

When you first run the query, you'll get everything that matches that query, with a change.type === "added". Then you will receive changes as they are made, one by one (unless someone writes a batch at once).

The way to manage this is to add a filter to the collection. For example, you may want to sort the collection by a date field or a name field. Then limit the results to a manageable number and paginate.

db.collection("cities")
    .where("state", ">=", "CA")
    .orderBy("state")
    .limit(50)
    .onSnapshot((snapshot) => {
        snapshot.docChanges().forEach((change) => {
            if (change.type === "added") {
                console.log("New city: ", change.doc.data());
            }
            if (change.type === "modified") {
                console.log("Modified city: ", change.doc.data());
            }
            if (change.type === "removed") {
                console.log("Removed city: ", change.doc.data());
            }
        });
    });

Don't forget to add an unsubscribe so that you can remove the listener