Possible to traverse the children of a Firebase node in reverse order?

Question

I'm looking into implementing an in-firebase index as described here: https://stackoverflow.com/a/10559689/534086, and trying to figure out how to deal with sorting data in descending order. Is it possible if you have a node with children 'a', 'b', 'c' to retrieve them 'c', 'b', 'a'? (while still being able to retrieve them in the original order as well?)

If it's not possible to traverse the node both forwards and backwards and I need to create two indexes, is their an easy algorithm for generating keys that sort in reverse lexographic order? For numbers, I think you can multiply by -1, but not sure how to handle strings...

Answer 1

It sounds like what you want is a "reverse()" query similar to how "limit()" works now. Firebase can't do this yet, but we're planning to add it.

Depending on your use case, it might be pretty simple for you to get around this though. If, for instance, you're using Firebase's sorting to keep a list in order that is being displayed to the user, you could simply modify the display logic to render things backward (prepend items instead of append for instance). If you're querying to select a window of data out of a large set of children (say, to get the first 10 items out of a long list), the sort order shouldn't be important -- your start and end points for the query will remain the same except they'll be reversed.