DCI + Rails new and create

dci-rest-creation.rb

# ---role

module BookManager
  def create_book(attrs)
    self.books.create! attrs
  end

  def update_book(book_id,attrs)
    book = self.books.find(book_id)
    book.update_attributes attrs
  end

  def delete_book(id)
    self.books.find(id).destroy
  end
end

# ---context

class BookModifyingContext
  attr_accessor :user, :book
  def initialize(user_id)
    @user = User.find(user_id)
    @user.extend BookManager
  end
end

class AddingBookContext < BookModifyingContext
  def execute(attrs)
    @user.create_book(attrs)
  end
end

class UpdateBookContext < BookModifyingContext
  def execute(id,attrs)
    @user.update_book(id,attrs)
  end
end

class DeletingBookContext < BookModifyingContext
  def execute(id)
    @user.delete_book(id)
  end
end

# ---controller

class BookController < ApplicationController
  def index
    @books = Book.all
  end

  def new
    @book = Book.new
  end

  def create
    AddBookContext.execute(params[:book])
  end

  def edit
    @book = Book.find(params[:id])
  end
  
  def update
    UpdateBookContext.execute(params[:id], params[:book])
  end
  
  def destroy
    DeleteBookContext.execute(params[:id])
  end
end

@dublinan BookManager extends the @user, not the context. The model User has expressed ActiveRecord association has_many :books which is not shown in that gist.