Hi ,

I want to insert user and company at once (user belongs to company, company can have many users) using Ecto.Multi. Here is my current form:

  <.simple_form :let={f} for={@changeset} action={~p"/users/register"}>
    <.inputs_for :let={company} field={f[:company]}>
      <.input field={company[:name]} type="text" label="Company" />
    </.inputs_for>

    <.input field={f[:email]} type="email" label="Email" required />
    <.input field={f[:password]} type="password" label="Password" required />

    <:actions>
      <.button phx-disable-with="Creating account..." class="w-full">Create an account</.button>
    </:actions>
  </.simple_form>

and Ecto.Multi transaction:

  def register(user_params, company_params) do
    Multi.new()
    |> Multi.run(:company, fn _repo, _changes ->
      case Companies.create_company(company_params) do
        {:ok, %{company: company}} -> {:ok, company}
        {:error, :company, changeset, _} -> {:error, changeset}
      end
    end)
    |> Multi.run(:user, fn _repo, %{company: company} ->
      user_params
      |> Map.put("company_id", company.id)
      |> Accounts.register_user()
    end)
    |> Repo.transaction()
  end

However if something went wrong while creating company (e.g. name was already taken) I got Company changeset, what causes an error: “could not generate inputs for :company from MyApp.Companies” (it expects User changeset). What is the most idiomatic approach in this case? I can’t use cast_assoc, since create_company is Multi transaction itself (it also invokes some additional steps).