I have a phoenix app with a lot of related tables. In particular, I have a regions (think territory) as a parent table that has a related child table consisting of 3-digit zip codes that are in a table region_zips.
I need a select form element in the region_zip form (created by phx.gen.html) in order to make sure I’m picking the correct region for a particular 3 digit zip code. I cannot get this to work no matter how many ways I’ve tried. I know the lookup in def new(conn, _params) works. It’s just not working in the form. I would greatly appreciate any assistance. Thanks in advance. Bill

def new(conn, _params) do
    regions = Regions.lookup_regions() #  Valid results are [%{id: 1, name: "Test" },...]
    changeset = RegionZips.change_region_zip(%RegionZip{})
    render(conn, :new, changeset: changeset, regions: regions)
  end

The related form is

<.simple_form :let={f} for={@changeset} action={@action}>
  <.error :if={@changeset.action}>
    Oops, something went wrong! Please check the errors below.
  </.error>
  <.input field={f[:region_id]} type="select" options={@regions} label="Region" />
  <.input field={f[:zip_prefix]} type="text" label="Zip prefix" />
  <:actions>
    <.button>Save Region zip</.button>
  </:actions>
</.simple_form>