Using Phoenix forms with Absinthe @graphql attribute in controller

I have finished reading Craft GraphQL APIs in Elixir with Absinthe (Pragprog) and I am trying to expand upon the item_controller.ex to allow for “menu item” editing.

I have made these functions in the controller:

  @graphql """
  query ($id: ID!) {
  menu_item(id: $id) @put {
  name
  description
  }
  }
  """
  def edit(conn, %{data: %{menu_item: item}}) do
    render(conn, "edit.html", item: item)
  end

  @graphql """
  mutation UpdateMenuItem($id: ID!, $input: MenuItemInput!) {
    updatedMenuItem: updateMenuItem(id: $id, input: $input) {
      errors { key message }
      menuItem {
        name
        description
        price
      }
    }
  }
  """
  def update(conn, %{data: %{menu_item: _}}) do
    conn
    |> redirect(to: "/admin/items")
  end
  def update(conn, %{errors: errors}) do
    conn
    |> put_flash(:info, Enum.reduce(errors, "", fn e, a -> a <> e.message end))
    |> redirect(to: "/admin/items")
  end

Here is my edit.html.eex:

<%= render "form.html",
Map.put(assigns, :action,
Routes.item_path(@conn, :update, @item)) %>

Here is my form.html.eex:

<%= form_for @conn, @action, [method: :put, as: :input], fn f -> %>
    <div class="form-group">
        <label for="description">Description</label>
        <input type="string" id="description" as="description" name="description" value="<%= @item.description %>"/>
        <label for="price">price</label>
        <input type="string" id="price" name="price" value="<%= @item.price %>"/>
        <label for="name">name</label>
        <input type="string" id="name" name="name" value="<%= @item.name %>"/>
        <label for="category">category</label>
        <input type="string" id="category" name="categoryId" value="<%= @item.category_id %>"/>
    </div>
    <%= submit "Update", class: "btn btn-primary" %>
<% end %>

But I get an error when I submit the form. This is the error:

In argument "input": Expected type "MenuItemInput!", found null.
Variable "input": Expected non-null, found null.

It makes sense to me. I could, for example change the name attribute of any of the input elements in form.html.eex to be "input" and then I would get a different error:

Argument "input" has invalid value $input.

Again, it makes sense to me. The $input argument is not a MenuItemInput variable.

So I am looking to approach this in either of 2 possible ways:

1. In the form.html.eex, I create a “form within a form” so that it has an “input” field which, in turn, has several fields.

2. In the item_controller I pass variables into the @graphql module attribute. I simply don’t know how to do this. I experimented with a lot of strange syntax because I cannot even find examples of SDL that have the variables inline.

Any advice/criticism/ideas are very welcome. I’m sure somebody else has done this since it seems like a natural thing to try after finishing the book.