I’m trying to sum only the copies_sold of :studio albums using an aggregate, but I’m not sure how to apply a filter to the joined records.

Here’s a simplified version of my resource:

def AshPg.Music.Artist do
  ...

  aggregates do
    sum :studio_copies_sold, [:albums], :copies_sold do
      # Invalid reference albums.type
      # filter expr(albums.type == :studio)

      # Not working
      join_filter [:albums], expr(type == :studio)
    end
  end
end

And here’s a test that creates an artist with multiple albums, where only one is of type :studio. The aggregate should return 1_000_000, but currently it’s returning the total sum of all album types.

defmodule AshPg.Music.ArtistTest do
  ...

  test "solo_copies_sold" do
    artist =
      Music.create_artist!(%{
        name: "250",
        albums: [
          %{title: "Rear Window", type: :single, copies_sold: 1000},
          %{title: "Bang Bus", type: :single, copies_sold: 2000},
          %{title: "뽕", type: :studio, copies_sold: 1_000_000}
        ]
      })

    %{studio_copies_sold: studio_copies_sold} = artist |> Ash.load!([:studio_copies_sold])

    # The sum of copies sold for studio albums should be 1_000_000
    assert studio_copies_sold == 1_000_000
  end
end

join_filter doesn’t seem to have any effect.

https://github.com/nallwhy/ash_pg/commit/4a84d244554620cb4ff602e9dcaa12bcaccf591d

Is there a correct way to apply a filter to aggregates based on joined relationships? Any help would be appreciated.