An excersie in removing duplication on CRUD Rails controllers. Inspired by the book Growing Rails Application in Practice

admin_base_controller.rb

# app/controllers/admin/base.rb

class Admin::BaseController
  include Admin::CRUDMethods
  
  class NotImplementedError < StandardError; end
  
  def index
    list_resources
  end
  
  def new
    build_resource
  end
  
  def create
    build_resource(accepted_params)
    save_resource
  end
  
  def show
    load_resource(id_key)
  end
  
  def edit
    load_resource(id_key)
  end
  
  def update
    load_resource(id_key)
    update_resource(accepted_params)
  end
  
  def destroy
    delete_resource(id_key)
  end
  
  private
  
  def model
    fail(
      NotImplementedError,
      'Configure main ActiveRecord class to manage in this controller.'
    )
  end
  
  def model_key
    model.to_s.tableize.to_sym
  end
  
  def id_key
    params[:id]
  end
  
  def model_fields
    fail(
      NotImplementedError,
      'Configure permitted field names to pass to a record in this controller.'
    )
  end
  
  def accepted_params
    params.require(model_key).permit(model_fields)
  end
  
  def success_action
    fail(
      NotImplementedError,
      'Configure what to do when saving/updating a record succeeds.'
    )
  end
  
  def error_action(resource, view)
    @resource = resource
    flash[:error] = 'Something went wrong.'
    render view
  end
  
  def destroy_success_action
    fail(
      NotImplementedError,
      'Configure what to do when deleting a record succeeds.'
    )
  end
end

admin_crud_methods.rb

# app/controllers/admin/crud_methods.rb

module Admin
  module CRUDMethods
    def list_resources
      @resources = model.load
    end
    
    def build_resource(attrs = {})
      @resource = model.new(attrs)
    end
    
    def load_resource(id)
      @resource = model.find(id)
    end
    
    def save_resource
      if @resource.save
        success_action('Successfully created resource.')
      else
        error_action(@resource, :new)
      end
    end
    
    def update_resource(attrs)
      if @resource.update_attributes(attrs)
        success_action('Successfully updated resource.')
      else
        error_action(@resource, :edit)
      end
    end
    
    def delete_resource(id)
      load_resource(id)
      @resource.destroy
      destroy_success_action
    end
  end
end

sample_inherited_controllers.rb

# app/controllers/admin/books_controller.rb

class Admin::BooksController < Admin::BaseController
  private
  
  def model
    Book
  end
  
  def model_fields
    [:title, :author_name, :isbn, :price, :page_count, :etc]
  end
  
  def success_action(message)
    redirect_to admin_book_path(@resource), notice: message
  end
  
  def destroy_success_action(message)
    redirect_to admin_books_path, notice: message
  end
end

# app/controllers/admin/movies_controller.rb

class Admin::MoviesController < Admin::BaseController
  private
  
  def model
    Movie
  end
  
  def model_fields
    [:title, :director_name, :upc, :genre, :duration, :etc]
  end
  
  def success_action(message)
    redirect_to admin_movie_path(@resource), notice: message
  end
  
  def destroy_success_action(message)
    redirect_to admin_movies_path, notice: message
  end
end