Hey there

I was trying to adapt the Contexts Article using the Form Struct and to_form.

I ended up having problems to render the input

<.input
      field={@form[:categories]}
      type="select"
      multiple={true}
      options={category_options(@article)}
    />

It errors like this

** (Protocol.UndefinedError) protocol Phoenix.HTML.Safe not implemented for type Ecto.Changeset (a struct).

because the value of the field @form[:categories] contains a Category changeset, introduced by the change_article\2 function - which is taken from the Context Article

  def change_article(%Article{} = article, attrs \\ %{}) do
    categories = list_categories_by_id(attrs["categories"])

    article
    |> Repo.preload(:categories)
    |> Article.changeset(attrs)
    |> Ecto.Changeset.put_assoc(:categories, categories)
  end

Phoenix tries to render the value in the select component but the changeset doesn’t help much here

  def input(%{type: "select"} = assigns) do
    ~H"""
    <fieldset class="fieldset mb-2">
      <label>
        <span :if={@label} class="fieldset-label mb-1">{@label}</span>
        <select
          id={@id}
          name={@name}
          class={["w-full select", @errors != [] && "select-error"]}
          multiple={@multiple}
          {@rest}
        >
          <option :if={@prompt} value="">{@prompt}</option>
          {Phoenix.HTML.Form.options_for_select(@options, @value)}
        </select>
      </label>
      <.error :for={msg <- @errors}>{msg}</.error>
    </fieldset>
    """
  end

I guess, I understand the problem, but I’m unsure how to proceed from here. I wasn’t very successfull finding examples using to_form.

What should I change, the input template, the form template, the change_article function or something else?

Thank you for help <3