many to many relationships management.

# Resource
actions do
  create :create do
    primary? true
    accept [:subject, :status, :matchers, :frequency]
    argument :fetchers, {:array, :uuid}
    change manage_relationship(:fetchers, type: :append_and_remove)
  end

  update :update do
    primary? true
    accept [:subject, :status, :matchers, :frequency]
    argument :fetchers, {:array, :uuid}
    change manage_relationship(:fetchers, type: :append_and_remove)
    require_atomic? false
  end
end

relationships do
  many_to_many :fetchers, Scraper.Fetcher,
    through: Scraper.TemplateFetcherRelationship,
    source_attribute_on_join_resource: :template_id,
    destination_attribute_on_join_resource: :fetcher_id
end

# Form component
  defp assign_form(%{assigns: %{template: template}} = socket) do
    prepared_context = context(socket, as: "template", forms: [auto?: true])

    form =
      if template do
        template = template |> Ash.load!([:fetchers], context(socket))
        AshPhoenix.Form.for_update(template, :update, [{:params, %{fetchers: Enum.map(template.fetchers, & &1.id)}} | prepared_context])
      else
        Knabis.Scraper.Template
        |> AshPhoenix.Form.for_create(:create, [{:params, %{fetchers: []}} | prepared_context])
      end

    assign(socket, form: to_form(form))
  end

  <.input
    field={@form[:fetchers]}
    type="select"
    label="Fetchers"
    options={@fetcher_options}
    multiple={true}
    prompt="Select fetchers..."
    description="Choose one or more fetchers to associate with this template"
  />