Firestore — 仅获取大型同步集合中更改的文档

Question

I've read all of the questions below, and cannot find anything in the docs to describe how to sync a collection and receive only changed documents from a collection. I've got over 500 documents in my synced collection (using redux-saga-firebase syncCollection ) but usually only about 100 of them ever change. At any given time, even fewer will change, but I'm currently getting all 500+ documents back when even one changes, which results in 500+ reads. Not ideal, and will cost me at scale.

Here is my code using redux-saga-firebase, but a vanilla firebase code answer would also suffice. How can get a synchronized response that sends only the changed documents in the collection?

export function* getPlayersFromDb() {
  yield fork(
    rsf.firestore.syncCollection,
    'players',
    { successActionCreator: response => ({
            type: t.GET_PLAYERS_FROM_DB_SUCCESS,
            payload: [...response],
        }),
        failureActionCreator: () => ({
            type: t.GET_PLAYERS_FROM_DB_FAILURE,
            payload: [],
        }),
        transform: response => messageTransformer(response),
    }
);

}

Does Firestore sync only diff?

Realm syncing with large collection on Firestore - architectural questions / issues

How to avoid unnecessary Firestore reads with Cache

What exactly does Firestore synchronization do?

Answer 1

Firestore queries don't have a notion of querying "only things that have changed". You will need to create that notion on your own. The usual way to do this is by recording a timestamp in each document with the time it was last updated, then using that field in a range filter to get only documents updated since the latest update was received. You will need to track that latest update timestamp in the client. One possibility is to use the greatest timestamp seen in any document to date.

Answer 2

This is a great article explaining some tips.

A strategy here is to add a property on each document such as lastModified and .get() from the Firebase client cache and only query the server to get documents with a lastModified greater than the client cache document fetch timestamp.

https://medium.com/firebase-tips-tricks/how-to-drastically-reduce-the-number-of-reads-when-no-documents-are-changed-in-firestore-8760e2f25e9e