angular firebase google-cloud-firestore angularfire

Firestore SnapshotChanges - Listening for New Document

I am working on creating a realtime scrolling pagination service using Firestore. I plan to write it by loading in limit of 10 real-time documents to an array that will display on screen. When the loadMore() function is called, use the startAfter function to load 10 more non-realtime documents, etc. I got this idea from Firebase's Youtube Channel

The Idea... The Problem

Once I load in some real-time documents, I want to listen for new documents in realtime, adding them or updating them in the array. collectionRef.snapshotChanges() emits a DocumentChangeAction[]. A single object in the array looks like this:

{
   doc: n {Df: e, E_: t, kf: n, Mf: false, Of: false, …}
   newIndex: 0
   oldIndex: -1
   type: "added"
}

It notates the last event the object experienced was added. Great but it doesn't notate when an object was not-seen-in-this-query-before.-aka,-just-added-and-newly-loaded.

The Question Does anyone know how to find brand new objects in realtime via firestore?

Sidenote: I could be approaching pagination all wrong but I believe this is a responsible way to achieve the task (that is, if it can be done this way).

Solution

Firestore doesn't maintain any sense of what a "new" document is. It sounds like you should store a timestamp in each document that records when it was created. You can then use this timestamp in a range filter to query for documents that are "new" by your definition.

If your definition of "new" is any document greater than the greatest timestamp seen in from a prior query, then just use that timestamp value in your query. You can then listen to the results of that query to get any newer documents in real time.