Firebase Database - Add Index on "dynamic" child - firebase

Question

I'm using Firebase Database to store the scores of a game. All is working fine until I've decided to implement a "weekly score".
In order to be able to filter by score and then order by weekly, I'm storing the data in the following structure:
game_scores-weekly
2018-01-29
user_id: { score, date, bla, bla bla}
user_id: { score, date, bla, bla bla}
user_id: { score, date, bla, bla bla}
2018-02-05
user_id: { score, date, bla, bla bla}
user_id: { score, date, bla, bla bla}
So, this works just fine but I get that annoying warning every new week about performance issues due not having indexes on "game_scores-weekly/new_week" indexOn "score". Manually adding the index works... until the next week, so not an option.
"game_scores-weekly": {
"2018-02-19": {
".indexOn": ["score", "uid"]
},
"2018-02-12": {
".indexOn": ["score", "uid"]
}
}
Is there any way to specify somehow a wildcard in the date, so it works for any new date? or perhaps can I programatically create the new index every week, or is there any other solution I might have not thought about?
Also, thought of manually creating list of all weeks of the year and adding it in one go, but likely would be a limit?
Last, but not least, I'm only interested on current week and last week scores, anything older I'd like to keep it to have some historical data but I don't query it in the game, so could potentially get rid of indexes of older weeks.
Cheers!

Answer 1

Thanks to #Tristan for pointing me in the right direction.
I used the following code to define the index and now warning is gone:
"game_scores-weekly": {
"$date": {
".indexOn": ["score", "uid"]
}
}
Seems super obvious now but couldn't find anything clear in the documentation.
Note that $date could be any name really, seems like you can specify a variable value using any $identifier.