Assigns is not assigning attribute in custom core component

Phoenix Forum Questions / Help
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1

Background

I have a custom component in my LiveView, which is basically a group of checkboxes.
I want to add a new attribute to my custom component, however no matter what I do, I always get nil when accessing said attribute.

Code

core_components.ex

  @doc """
  Generate a checkbox group for multi-select.

  ## Examples

    <.checkgroup
      field={@form[:genres]}
      label="Genres"
      options={[{"Fantasy", "fantasy"}, {"Science Fiction", "sci-fi"}]}
      selected={[{"Fantasy", "fantasy"}]}
    />

  """
  attr :id, :any
  attr :name, :any
  attr :label, :string, default: nil
  attr :field, Phoenix.HTML.FormField, doc: "a form field struct retrieved from the form, for example: @form[:genres]"
  attr :errors, :list
  attr :required, :boolean, default: false
  attr :rest, :global, include: ~w(form readonly)
  attr :class, :string, default: nil
  attr :options, :list, default: [], doc: "the options to pass to Phoenix.HTML.Form.options_for_select/2"
  attr :selected, :list, default: [], doc: "the currently selected options, to know which boxes are checked"

  attr :meow, :any, default: "meow", doc: "a very cool new attribute!"

  def checkgroup(assigns) do
    new_assigns =
      assigns
      |> assign(:multiple, true)
      |> assign(:type, "checkgroup")

    input(new_assigns)
  end


  def input(%{type: "checkgroup"} = assigns) do
    ~H"""
    <p> <%= "Cat says: #{@meow}" %></p> 

    <div class="mt-2">
      <%= for opt <- @options do %>
        <div class="relative flex gap-x-3">
          <div class="flex h-6 items-center">
            <input id={opt.id} name={@name} type="checkbox" value={opt.id} checked={opt in @selected} disabled={false} />
          </div>
          <div class="text-sm leading-6">
            <label  for={opt.id} ><%= opt.name %></label>
          </div>
        </div>

      <% end %>
    </div>
    """
  end

Here I am using a customer component to render a stylish checkbox group. It works fine, except for the :meow attribute, which somehow is always nil when inside the input function.

Error

Using this code as a sample:

<.checkgroup field={@form[:my_form]} label="SUper question!" options={@sounds} selected={@selected_sounds} meow={[1, 2]} required />

I get the following error upon rendering this code:

** (exit) an exception was raised:
    ** (KeyError) key :meow not found in: %{
  __changed__: nil,
  __given__: %{
    __changed__: nil,
    __given__: %{
      __changed__: nil,
      __given__: %{
        __changed__: nil,
        field: %Phoenix.HTML.FormField{
          id: "my_form",
          name: "my_form",
          errors: [],
          field: :my_form,
          form: %Phoenix.HTML.Form{
            source: %{"some_command" => []},
            impl: Phoenix.HTML.FormData.Map,
            id: nil,
            name: nil,
            data: %{},
            hidden: [],
            params: %{"some_command" => []},
            errors: [],
            options: [],
            index: nil,
            action: nil
          },
          value: nil
        },
        label: "SUper question!",
        meow: [1, 2],
        options: [1, 2, 3, 4],
        # .... more things follow

As you can see, meow: [1, 2], is clearly present. Yet, @meow returns nil and using assigns.meow outright crashes the application.

What am I doing wrong here and how can I fix it?

2

It’s saying :meow isn’t found inside a map only has the keys :__changed__ and :__given__ at its root, so that makes sense. It looks like there is some odd recursion going on in the map assignment as you those two meta keys are getting nested a couple of times. Is there any intermediary code you haven’t shared that might help diagnose? One thing that does stand out is that your attr calls are now tied to checkbox and input does have any, though perhaps you just left those out for the example. It may be as simple as changing def checkgroup to def input. This is more inline with the generated API anyway where everything is an input with a type.

3

No intermediary code. All the things done here are done by the Phoenix framework.

I am confused. I have created a component, checkgroup. Yes, I do use the input function, but I pass it the type (type: checkgroup) as well, so I don’t understand how this can be an issue.

If the input function does magic behind the scenes (which maybe it does) then that would explain the behaviour, but other than that I am quite lost.

I very much like the API of .checkgroup, for a checkgroup is not an input, but a collection of connected inputs. I based this code on this tutorial:

4

I did find another input function from core_components that is run before my final function:

  def input(%{field: %Phoenix.HTML.FormField{} = field} = assigns) do
    assigns
    |> assign(field: nil, id: assigns.id || field.id)
    |> assign(:errors, Enum.map(field.errors, &translate_error(&1)))
    |> assign_new(:name, fn -> if assigns.multiple, do: field.name <> "[]", else: field.name end)
    |> assign_new(:value, fn -> field.value end)
    |> input()
  end

I guess I could change this one, but I am not sure if there is a better way.

5

After a lot of digging around, i realized that all of the input functions deal with assigns. This meant that some things are being done that I dont fully understand, not control.

I decided to move away from using/modifying the input functions and created my own component from scratch:

@doc """
  Generate a checkbox group for multi-select.

  ## Examples

    <.checkgroup
      field={@form[:genres]}
      label="Genres"
      options={[{"Fantasy", "fantasy"}, {"Science Fiction", "sci-fi"}]}
      selected={[{"Fantasy", "fantasy"}]}
    />

  """
  attr :name, :any

  attr :field, Phoenix.HTML.FormField,
    doc: "a form field struct retrieved from the form, for example: @form[:genres]"

  attr :required, :boolean, default: false

  attr :options, :list,
    default: [],
    doc: "the options to pass to Phoenix.HTML.Form.options_for_select/2"

  attr :disabled, :list, default: [], doc: "the list of options that are disabled"

  attr :selected, :list,
    default: [],
    doc: "the currently selected options, to know which boxes are checked"

  def checkgroup(%{field: %Phoenix.HTML.FormField{} = field} = assigns) do
    assigns =
      assigns
      |> assign(:name, "#{field.name}[]")

    ~H"""
    <div class="mt-2">
      <%= for opt <- @options do %>
        <div class="relative flex gap-x-3">
          <div class="flex h-6 items-center">
            <input
              id={opt.id}
              name={@name}
              type="checkbox"
              value={opt.id}
              class={
                if opt in @disabled do
                  "h-4 w-4 rounded border-gray-300 text-gray-300 focus:ring-indigo-600"
                else
                  "h-4 w-4 rounded border-gray-300 text-indigo-600 focus:ring-indigo-600"
                end
              }
              checked={opt in @selected}
              disabled={opt in @disabled}
            />
          </div>
          <div class="text-sm leading-6">
            <label
              for={opt.id}
              class={
                if opt in @disabled do
                  "text-base font-semibold text-gray-300"
                else
                  "text-base font-semibold text-gray-900"
                end
              }
            >
              <%= opt.name %>
            </label>
          </div>
        </div>
      <% end %>
    </div>
    """
  end

which works as expected and all the assigns not have the expected values.

1 Like
6

Crap, sorry, I was working on a response to this a few days ago and got distracted :grimacing: Sorry about that! Glad you solved it!

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