Query multiple subcollections firestore flutterfire

Question

Im working on a project using flutter and firebase, currently the database(firestore) has A collection named Projects , each project has an owner(userId) and a subcollection named Sections and each section has an Items collection. Each Item has a list of tags (strings). I wanted to add a search Items by tag feature, but just realized that the nested collections structure makes it hard. Changing the database structure now would be a lot of work. Is there a way to apply a query to multiple subcollections? basically I would need to query all projects owned by the user then query for all in those projects sections and then all todos inside them that contain a certain tag. I don`t want to do multiple queries and join them with frontend code because I'm using real time functionality and having to deal with multiple streams isn't ideal. Cloud functions aren't an option right now because I'm using the free plan.

Answer 1

You're looking for a so-called collection group query , which searches across all collections with a certain name in one go.