Firebase Data Desc Sorting in Android

Question

I am storing data in Firebase storage.

Object Comment with attribute timestamp. When I push data from device to Firebase I'm populating timestamp with currentTime and store in long data type.

When I do retrieving the data with firebaseRef.orderByChild("timestamp").limitToLast(15) result is not sorting how I expected.

I even played around with rules and no result:

{
    "rules": {
        ".read": true,
        ".write": true,
        ".indexOn": "streetrate",
        "streetrate": {
          ".indexOn": ".value"
        }
    }
}

I tried store timestamp in String data type, same issue.

Answer 1

Firebase can order the items in ascending order by a given property and then returns either the first N items (limitToFirst()) or the last N items (limitToLast()). There is no way to indicate that you want the items in descending order.

There are two options to get the behavior you want:

1. Use a Firebase query to get the correct data, then re-order it client-side

2. Add a field that has a descending value to the data

For the latter approach, it is common to have a inverted timestamp.

-1 * new Date().getTime();