add array enum support

[davorbadrov]

Hi, and thanks for the lib. I've been using it in a few projects and it's quite handy.

I've noticed that it doesn't support {:array, :enum} definitions, like the following:

  defparams :arary_list_example do
    required :array_list, {:array, :enum}, rules: [values: [:active, :inactive]]
    required :array_list_2, {:array, :enum}, rules: [values: [:active, :inactive], min: 1]
  end

This PR adds the support and a few tests showing how they're used. Let me know if this is something you'd want merged and if any changes are required. I'm willing to add examples to the docs as well.

[martinthenth]

Hi @davorbadrov! Thanks for your PR. I am interested in knowing more about the use-cases and whether they fit in the existing features (like an array of strings)

[davorbadrov]

Hi Martin,

my usage of the lib is for form validations mainly, but I'm also experimenting for using it for scenarios where I'm passing maps into internal business logic, to ensure that they're adhering to a strict contract.

For form validations, when working with multiselects or something similar, this can both validate and parse the incoming values from HTML forms into atoms.

# Here's how I use it currently
defmodule App.UserRegistrationLive do
  # ...
  use Goal
  
  defparams :registration_form do
    required(:email, :string)
    required(:password, :string)
    required(:subscriptions, {:array, :string}, min: 1, rules: [included: ["marketing", "critical", "some_other_value"]])
  end

  def handle_event("register", params, socket) do
    with {:ok, attrs} <- validate(:registration_form, params),
        {:ok, attrs} <- convert_subscriptions_to_atoms(attrs),
        {:ok, user} <- register_user(attrs) do
      {:noreply, assign(socket, user_registered: true)}
    else
      error ->
        handle_error_response(socket, params, error, &assign_unsubscribe_sms_form/3)
    end
  end
  
  def convert_subscriptions_to_atoms(attrs) do
    # Here I need to manually convert the subscriptions to atoms,
    # make sure to use the String.to_existing_atom/1
    # ensure there's at least a single item in there,
    # and that the field consists of a valid set of items,
    # if something's amiss, then I need to create a changeset with an error here.
    #
    # Everything that Goal usually does, expect it doesn't do it with an array of enums.
  end
  
  @spec register_user(%{
    email: String.t(),
    password: String.t(),
    subscriptions: [UserSubscription.t()]
  }) :: {:ok, User.t()} | {:error, Ecto.Changeset.t()}
  def register_user(user_attrs) do
    # ...
  end

  # ...
end

# This would be the preferred approach
defmodule App.UserRegistrationLive do
  # ...
  use Goal
  
  defparams :registration_form do
    required(:email, :string)
    required(:password, :string)
    required(:subscriptions, {:array, :enum}, min: 1, rules: [values: [:marketing, :critical, :some_other_value]])
  end

  def handle_event("register", params, socket) do
    with {:ok, attrs} <- validate(:registration_form, params),
         # no need for manual conversion here
         {:ok, user} <- register_user(attrs) do
      {:noreply, assign(socket, user_registered: true)}
    else
      error ->
        handle_error_response(socket, params, error, &assign_unsubscribe_sms_form/3)
    end
  end
  
  @spec register_user(%{
    email: String.t(),
    password: String.t(),
    subscriptions: [UserSubscription.t()]
  }) :: {:ok, User.t()} | {:error, Ecto.Changeset.t()}
  def register_user(user_attrs) do
    # ...
  end

  # ...
end

[martinthenth]

Thanks for the example, it is an interesting use-case and worth implementing! I'll take a look at your code when I have some time

[martinthenth]

Looks good to me! Thanks for your contribution!