Automatically creating has_one child on parent creation

Questions / Help
, ,
7

Thanks, based off your suggestion I’ve written the following:

defmodule Parent do
  schema "parents" do
    has_one :child, Child, on_replace: :update
  end

  def changeset(%Parent{} = ch, attrs) do
    ch
    |> cast(attrs, [])
    |> cast_assoc(:child)
    |> changeset_preload(:child)
    |> put_assoc_nochange(:child, %{})
  end

  def changeset_preload(ch, field),
    do: update_in(ch.data, &Repo.preload(&1, field))

  def put_assoc_nochange(ch, field, new_change) do
    case get_field(ch, field) do
      nil -> put_assoc(ch, field, new_change)
      _ -> ch
    end
  end
end

changeset_preload/2 is based off this post.

Though I’m not sure if this is the best way to solve this problem, I’m pretty ok with the solution. Unfortunately, I have to put a preload for when put_assoc is called.