defmodule Hierarch.Query.Parent do
  import Ecto.Query

  @doc """
  Return query expressions for the parent
  """

  def query(%schema{} = struct) do
    parent_id =
      struct
      |> Hierarch.Util.struct_path()
      |> Hierarch.LTree.parent_id()

    [pk_column] = schema.__schema__(:primary_key)

    case parent_id do
      nil ->
        from(t in schema, where: 0 == 1)

      _ ->
        from(t in schema, where: field(t, ^pk_column) == ^parent_id)
    end
  end
end