Action Controller

Example: An action called articles#change_book

def change_book
  @target_book = current_user.books.find_by(id: params[:book_id])

  if !@target_book
    head :unprocessable_entity
  elsif @target_book == @book
    head :ok
  else
    # TODO: This has a bug I'm pretty sure where it can leave the ordinal positions
    # in a state that it needs to be fixed by the FixOrdinalPositionsJob
    @book.move_ordinal_child_to_new_parent(new_parent: @target_book, child: @article,
                                            new_ordinal_position: @target_book.articles_count)
    redirect_to book_articles_path(@book),
                flash: { notice: "#{@article.title} successfully moved to #{@target_book.title}" }
  end
end