I have a firebase real-time database with this structure :

With a web application I need to find al documents in files that have a label that startsWith per.

In the example in attached I suppose to receive at least a document with id -O18Yjm1awCNcF-gSvYf.

I don’t have a lot of experience with noSql database and no-experience with firebase, and with the documentation that I found seems that is not possible with query but only looping the responses. Which is the best way? Maybe refactor the data-structure duplicating the informations?