How to get Rails' radio buttons to work.

index.haml

%ul
  - @omghis.each do |omghi|
    %li
      = omghi.wtf
      = image_tag omghi.media.variant(resize: "339x243") if omghi.media.present?

:css
  .omgsection { border: 1px solid black; }

= form_for @omghi, controller: :omghi, method: :create do |f|
  .omgsection
    = f.label :wtf
    = f.text_field :wtf

  .omgsection
    - @images.each do |image|
      %div
        = f.radio_button :media_filename, image
        = f.label :media_filename, value: image do
          = image_tag image

  .omgsection
    = f.submit 'Create!'

migration.rb

class AddOmghis < ActiveRecord::Migration[6.0]
  def change
    create_table :omghis do |t|
      t.string :wtf
    end
  end
end

omghi.rb

class Omghi < ApplicationRecord
  has_one_attached :media

  validates :wtf, presence: true

  def media_filename
    return '' if media.blank?
    media.filename.to_s
  end
end

omghi_controller.rb

class OmghiController < ApplicationController
  before_action do
    @omghis = Omghi.all
    @images = ['avatar_01.png', 'avatar_02.png',]
  end

  def index
    @omghi = Omghi.new
  end

  def create
    omghi_params = params.require(:omghi).permit(:wtf, :media_filename)
    basename     = File.basename omghi_params.delete(:media_filename).to_s
    path         = Rails.public_path/'images'/basename
    @omghi       = Omghi.new(omghi_params)
    @omghi.media.attach io: path.open, filename: path.basename if path.exist?
    if @omghi.save
      redirect_to omghis_path
    else
      render :index
    end
  end
end

routes.diff

+  get  '/omghi', to: 'omghi#index',  as: :omghis
+  post '/omghi', to: 'omghi#create'