Firestore Query Data Order

Question

I am retrieving data from Firestore and I want to add an order of retrieving it, so I have tried this code:

 Query query = firebaseFirestore.collection("docs").orderBy("date", Query.Direction.DESCENDING/*ASCENDING*/);
    FirestoreRecyclerOptions<download> docsFirestoreRecyclerOptions = new FirestoreRecyclerOptions.Builder<download>()
            .setQuery(query, download.class)
            .build();

In date, I am adding time and date in String type like

02:42:31 - 2020/08/01

by this, I want to make sure the newest post appears on the top of recycler view. it works well in this day but the next day if the time let's say

01:00:00 - 2020/08/02

It is will appear before the post that added the previous day. Is there a better way to ordering data from Firestore?

Answer 1

Is there a better way to ordering data from Firestore?

Sure it is. Instead of storing the time and date as a String, you can store it either as a Java Date, the Date being a Firestore supported data type or as a Firestore Timestamp object. Here is an answer that can help you achieve that:

ServerTimestamp is always null on Firebase Firestore

Now, having the type of the date property as Firestore Timestamp, your query will work perfectly fine.

However, if you insist to store the dates and times as Strings, the option that you have is to store them in a format that can be sorted lexicographical and chronological at the same time.

The ISO 8601 format looks like this:

20200802T131425

That's the current time I'm answering this question.

August 02, 2020 1:14:25 PM UTC