categories_controller.rb

module Admin
  class CategoriesController < BaseController
    def new
      @form = CategoryForm.new
    end
    
    def create
      @form = CategoryForm.new(params[:category])

      if @form.valid?
        category = CreatesCategory.new(
          @form.attributes.merge(company_id: current_company.id)
        ).call
        show_notice
        redirect_to admin_category_products_path(category.id)
      else
        render :new
      end
    end
  end
end

category_form.rb

class CategoryForm
  include FunkyForm

  IMAGES = %w(
    not_important
  )

  model "Category"

  attribute :id, Integer
  attribute :name, String
  attribute :image, String, default: IMAGES.first

  validates :name, presence: true, length: {within: 3..20}
  validates :image, presence: true, inclusion: {in: IMAGES}
end

new.html.slim

= simple_form_for [:admin, @form], html: {class: "form-horizontal"} do |f|
  = f.input :name, placeholder: "Category name"

  = f.input :image, as: :hidden

  .control-group.string.required
    = f.label :image
    .controls.category-images
      - CategoryForm::IMAGES.each do |image|
        / removed

  .form-actions
    = f.button :submit, class: "btn-primary"