How to retrieve 1 document from firebase/firestore collection based on date in dart/flutter?

Question

Ofc, I know the basic way we retrieve a whole bunch of documents from a collection like so:

      stream: Firestore.instance
          .collection("collection_name")
          .orderBy("date", descending: true) // new entries first
          .snapshots(),
      builder: (context, snapshot) { ....

This is fine when I'm displaying a whole bunch of data.

But I have situation where I need to do some calculations with the last added numbers, meaning I just need to get 1 document, so I what I do is sort data by date and limit by 1, then make the query for this one document like this

List<DocumentSnapshot> list;
    QuerySnapshot querySnapshots;
    if (await AuthHelper.checkIfUserIsLoggedIn()) {
      String userId = await AuthHelper.getUserID();
      querySnapshots = await Firestore.instance
          .collection("collection_name")
          .orderBy("date", descending: true) // new entries first, date is one the entries btw
          .limit(1)
          .getDocuments(); // Get Documents not as a stream
      list = querySnapshots.documents; // Make snapshots into a list
      return (list ?? null);
    } else {
      return null;
    }

But is this the best way to do it ? When making this query aren't I getting the whole set of documents and discarding the rest ? Which means when this collections grows this is going get slower and slower ?

Is there a better way to retrieve the last added document ? So I can use it as list/array/map and not as stream ?

Thanks.

Answer 1

When you limit the query, you are only ever going to read that number of documents maximum . It's not going to read the entire collection and discard the extras.