Rails form example using Virtus and ActiveModel

_form_errors.html.erb

<% if form.errors.full_messages.length.positive? %>
  <ul>
  <% form.errors.full_messages.each do |message| %>
    <li><%= message %></li>
  <% end %>
  </ul>
<% end %>

base_form.rb

class BaseForm
  include ActiveModel::Model
  include Virtus.model

  def save
    return false unless valid?

    # you would just override this method in any class
    # inheriting from BaseForm
    save_form
  end
end

book_form.html.erb

<%= form_for(@facade.form, url: @facade.form.id.present? ? book_path(@facade.form.id) : book_new_path, method: @facade.form.id.present? : :patch : :post) do |f| %>
  <%= render 'form_errors', form: @facade.form %>
  <div class="form-group">
    <%= f.label :title %>
    <%= f.text_field :title, required: true %>
  </div>
  <div class="form-group">
    <%= f.label :isbn %>
    <%= f.text_field :isbn, required: true %>
  </div>
  <div class="form-group">
    <%= f.label :author %>
    <%= f.text_field :author, required: true %>
  </div>
  <div class="form-group">
    <%= f.label :genre %>
    <%= f.select :genre, options_for_select(@facade.genre_options, @facade.form.genre), { prompt: 'Please Select' }, required: true %>
  </div>
  <%= f.hidden_field :id, value: @facade.form.id %>
  <div class="form-group">
    <%= f.submit %>
  </div>
<% end %>

book_upsert_form.rb

class BookUpsertForm < BaseForm
  validates_with ISBNFormatValidator
  
  attribute :id, Integer
  attribute :title, String
  attribute :isbn, String
  attribute :author, String
  
  validate :title, :isbn, :author, presence: true

  def save_form
    Book.transaction do
      commit_book_changes
      enqueue_background_job
    end
  end
  
  private
  
  def commit_book_changes
    return Book.update(id, attributes.except(:id)) if id.present?
    @id = Book.create(attributes).id
  end
  
  def enqueue_background_job
    Resque.enqueue(BookChangeNotifier, id)
  end
end

books_controller.rb

class BooksController < ApplicationController
  def new
    # form logic is inside the facade
    @facade = BookUpsertFacade.new
  end
  
  def create
    @facade = BookUpsertFacade.new(params)
    return redirect_to(book_path(@facade.form.id)) if @facade.form.save
    flash[:warning] = 'There were validation errors encountered when creating the book'
    render :new
  end
  
  def edit
    @facade = BookUpsertFacade.new(params)
  end
  
  def update
    @facade = BookUpsertFacade.new(params)
    return redirect_to(book_path(@facade.form.id)) if @facade.form.save
    flash[:warning] = 'There were validation errors encountered when updating the book'
    render :edit
  end
end

isbn_format_validator.rb

class ISBNFormatValidator < ActiveModel::Validator
  def validate(record)
    return if ISBNFormatCheck.format_ok?(isbn)
    errors.add(:base, 'ISBN is in an invalid format')
  end
end