java - Cloud Firestore - How to get relational data from two collections?

Question

I want to define these two collections in Cloud Firestore. Some sample data has been shown below:

Playlists:

• name: "playlist1"
• songCount: //To be calculated on real time

Songs:

• title: "song1"

• playlistId: "playlist1"

• title: "song2"

• playlistId: "playlist1"

• title: "song3"

• playlistId: "playlist1"

Further, in my Android app, I want to show separate lists of all playlists and all songs. However, while displaying the list of all playlists, I want to show the name of each playlist alongwith the number of songs contained in each, based on the value in "songCount".

Please advise what sort of query I need to make in Cloud Firestore to achieve this objective. Is there a JOIN function available or would I have to put the Songs collection in a loop and count the ones having playlistId as "playlist1", and then repeat it for all the playlists that are to be presented in the list of playlists? I want to have a smarter solution but couldn't find one on the internet.

Any help would be a great help. Thanks for your time.

Answer 1

Waitting for answers