Ash Framework

Who Do You Follow?

With our shiny new relationships in place, we can use them to determine if a given user follows a given artist and show that information in the app.

We’ll write this as a custom calculation, as an expression that uses the exists^[177] sub-expression. exists lets us check if any records in a relationship match a given condition, so we can use it to check if any of an artist’s followers are the current user, the actor running this query.

This will be loaded as part of an Artist record and shown on the artist profile page, so the calculation can be put on the Tunez.Music.Artist resource:

09/lib/tunez/music/artist.ex

calculations do
  calculate :followed_by_me,
            :boolean,
 expr(exists(follower_relationships, follower_id ...