rethink_people.ex

def get_if_related_to(id, relationship) do  
  table("people") |> filter(lambda fn (person) ->
    case relationship do
      r when r in [:brother, :sister] ->
        person[:siblings] |> contains(id)
      r when r in [:mother, :father] ->
        person[:children] |> contains(id)
      r when r in [:son, :daughter] ->
        table("people")
          |> get(id)
          |> get_field("children")
          |> contains(person[:id])
      r when r in [:aunt, :uncle] ->
        person[:siblings]
          |> flat_map(fn sibling ->
            sibling |> get_field("children")
          end) |> contains(id)
    end
  end)
end