ash_postgres/test/rel_with_parent_filter_test.exs

defmodule AshPostgres.RelWithParentFilterTest do
  use AshPostgres.RepoCase, async: false

  alias AshPostgres.Test.{Api, Author}

  require Ash.Query

  test "filter on relationship using parent works as expected when used in aggregate" do
    %{id: author_id} =
      Author
      |> Ash.Changeset.for_create(:create, %{first_name: "John", last_name: "Doe"})
      |> Api.create!()

    Author
    |> Ash.Changeset.for_create(:create, %{first_name: "John"})
    |> Api.create!()

    # here we get the expected result of 1 because it is done in the same query
    assert %{num_of_authors_with_same_first_name: 1} =
             Author
             |> Ash.Query.for_read(:read)
             |> Ash.Query.filter(id == ^author_id)
             |> Ash.Query.load(:num_of_authors_with_same_first_name)
             |> Api.read_one!()
  end

  test "filter on relationship using parent works as expected when loading relationship" do
    %{id: author_id} =
      Author
      |> Ash.Changeset.for_create(:create, %{first_name: "John", last_name: "Doe"})
      |> Api.create!()

    Author
    |> Ash.Changeset.for_create(:create, %{first_name: "John"})
    |> Api.create!()

    assert %{authors_with_same_first_name: authors} =
             Author
             |> Ash.Query.for_read(:read)
             |> Ash.Query.filter(id == ^author_id)
             # right now it first loads the contact
             # then it loads the relationship
             # but when doing that it does a inner lateral join
             # instead of using the id from the parent relationship
             |> Ash.Query.load(:authors_with_same_first_name)
             |> Api.read_one!()

    assert length(authors) == 1
  end
end