对于如下代码:

class WeblogController < ActionController::Base
  scaffold :entry
end

这将生成如下代码:

class WeblogController < ActionController::Base

  verify :method => :post, \:only => [ :destroy, :create, :update ],
         :redirect_to => { :action => :list }

  def index
    list
  end

  def list
    @entries = Entry.find(:all)
    render_scaffold "list"
  end

  def show
    @entry = Entry.find(params[:id])
    render_scaffold
  end

  def destroy
    Entry.find(params[:id]).destroy
    redirect_to :action => "list"
  end

  def new
    @entry = Entry.new
    render_scaffold
  end

  def create
    @entry = Entry.new(params[:entry])
    if @entry.save
      flash[:notice] = "Entry was successfully created"
      redirect_to :action => "list"
    else
      render_scaffold('new')
    end
  end

  def edit
    @entry = Entry.find(params[:id])
    render_scaffold
  end

  def update
    @entry = Entry.find(params[:id])
    @entry.attributes = params[:entry]
    if @entry.save
      flash[:notice] = "Entry was successfully updated"
      redirect_to :action => "show", :id => @entry
    else
      render_scaffold('edit')
    end
  end

end

原来scaffolding是一个Rails的插件，源码如下:

module Scaffolding # :nodoc:
  def self.included(base)
    base.extend(ClassMethods)
  end

  # Scaffolding is a way to quickly put an Active Record class online by providing a series of standardized actions
  # for listing, showing, creating, updating, and destroying objects of the class. These standardized actions come
  # with both controller logic and default templates that through introspection already know which fields to display
  # and which input types to use. Example:
  #
  #  class WeblogController < ActionController::Base
  #    scaffold :entry
  #  end
  #
  # This tiny piece of code will add all of the following methods to the controller:
  #
  #  class WeblogController < ActionController::Base
  #    verify :method => :post, \:only => [ :destroy, :create, :update ],
  #           :redirect_to => { :action => :list }
  #
  #    def index
  #      list
  #    end
  #
  #    def list
  #      @entries = Entry.find(:all)
  #      render_scaffold "list"
  #    end
  #
  #    def show
  #      @entry = Entry.find(params[:id])
  #      render_scaffold
  #    end
  #
  #    def destroy
  #      Entry.find(params[:id]).destroy
  #      redirect_to :action => "list"
  #    end
  #
  #    def new
  #      @entry = Entry.new
  #      render_scaffold
  #    end
  #
  #    def create
  #      @entry = Entry.new(params[:entry])
  #      if @entry.save
  #        flash[:notice] = "Entry was successfully created"
  #        redirect_to :action => "list"
  #      else
  #        render_scaffold('new')
  #      end
  #    end
  #
  #    def edit
  #      @entry = Entry.find(params[:id])
  #      render_scaffold
  #    end
  #
  #    def update
  #      @entry = Entry.find(params[:id])
  #      @entry.attributes = params[:entry]
  #
  #      if @entry.save
  #        flash[:notice] = "Entry was successfully updated"
  #        redirect_to :action => "show", :id => @entry
  #      else
  #        render_scaffold('edit')
  #      end
  #    end
  #  end
  #
  # The <tt>render_scaffold</tt> method will first check to see if you've made your own template (like "weblog/show.erb" for
  # the show action) and if not, then render the generic template for that action. This gives you the possibility of using the
  # scaffold while you're building your specific application. Start out with a totally generic setup, then replace one template
  # and one action at a time while relying on the rest of the scaffolded templates and actions.
  module ClassMethods
    # Adds a swath of generic CRUD actions to the controller. The +model_id+ is automatically converted into a class name unless
    # one is specifically provide through <tt>options[:class_name]</tt>. So <tt>scaffold :post</tt> would use Post as the class
    # and @post/@posts for the instance variables.
    #
    # It's possible to use more than one scaffold in a single controller by specifying <tt>options[:suffix] = true</tt>. This will
    # make <tt>scaffold :post, :suffix => true</tt> use method names like list_post, show_post, and create_post
    # instead of just list, show, and post. If suffix is used, then no index method is added.
    def scaffold(model_id, options = {})
      options.assert_valid_keys(:class_name, :suffix)

      singular_name = model_id.to_s
      class_name    = options[:class_name] || singular_name.camelize
      plural_name   = singular_name.pluralize
      suffix        = options[:suffix] ? "_#{singular_name}" : ""

      unless options[:suffix]
        module_eval <<-"end_eval", __FILE__, __LINE__
          def index
            list
          end
        end_eval
      end

      module_eval <<-"end_eval", __FILE__, __LINE__

        verify :method => :post, \:only => [ :destroy#{suffix}, :create#{suffix}, :update#{suffix} ],
               :redirect_to => { :action => :list#{suffix} }


        def list#{suffix}
          @#{singular_name}_pages, @#{plural_name} = paginate :#{plural_name}, :per_page => 10
          render#{suffix}_scaffold "list#{suffix}"
        end

        def show#{suffix}
          @#{singular_name} = #{class_name}.find(params[:id])
          render#{suffix}_scaffold
        end

        def destroy#{suffix}
          #{class_name}.find(params[:id]).destroy
          redirect_to :action => "list#{suffix}"
        end

        def new#{suffix}
          @#{singular_name} = #{class_name}.new
          render#{suffix}_scaffold
        end

        def create#{suffix}
          @#{singular_name} = #{class_name}.new(params[:#{singular_name}])
          if @#{singular_name}.save
            flash[:notice] = "#{class_name} was successfully created"
            redirect_to :action => "list#{suffix}"
          else
            render#{suffix}_scaffold('new')
          end
        end

        def edit#{suffix}
          @#{singular_name} = #{class_name}.find(params[:id])
          render#{suffix}_scaffold
        end

        def update#{suffix}
          @#{singular_name} = #{class_name}.find(params[:id])
          @#{singular_name}.attributes = params[:#{singular_name}]

          if @#{singular_name}.save
            flash[:notice] = "#{class_name} was successfully updated"
            redirect_to :action => "show#{suffix}", :id => @#{singular_name}
          else
            render#{suffix}_scaffold('edit')
          end
        end

        private
          def render#{suffix}_scaffold(action=nil)
            action ||= caller_method_name(caller)
            # logger.info ("testing template:" + "\#{self.class.controller_path}/\#{action}") if logger

            if template_exists?("\#{self.class.controller_path}/\#{action}")
              render :action => action
            else
              @scaffold_class = #{class_name}
              @scaffold_singular_name, @scaffold_plural_name = "#{singular_name}", "#{plural_name}"
              @scaffold_suffix = "#{suffix}"
              add_instance_variables_to_assigns

              @template.instance_variable_set("@content_for_layout", @template.render_file(scaffold_path(action.sub(/#{suffix}$/, "")), false))

              if !active_layout.nil?
                render :file => active_layout, :use_full_path => true
              else
                render :file => scaffold_path('layout')
              end
            end
          end

          def scaffold_path(template_name)
            File.dirname(__FILE__) + "/templates/" + template_name + ".erb"
          end

          def caller_method_name(caller)
            caller.first.scan(/`(.*)'/).first.first # ' ruby-mode
          end
      end_eval
    end
  end
end

现在的scaffolding源码在$RUBY_HOME\lib\ruby\gems\1.8\gems\actionpack-1.13.3\lib\action_controller\scaffolding.rb:

module ActionController
  module Scaffolding # :nodoc:
    def self.included(base)
      base.extend(ClassMethods)
    end

    # Scaffolding is a way to quickly put an Active Record class online by providing a series of standardized actions
    # for listing, showing, creating, updating, and destroying objects of the class. These standardized actions come
    # with both controller logic and default templates that through introspection already know which fields to display
    # and which input types to use. Example:
    #
    #  class WeblogController < ActionController::Base
    #    scaffold :entry
    #  end
    #
    # This tiny piece of code will add all of the following methods to the controller:
    #
    #  class WeblogController < ActionController::Base
    #    verify :method => :post, \:only => [ :destroy, :create, :update ],
    #           :redirect_to => { :action => :list }
    #
    #    def index
    #      list
    #    end
    #
    #    def list
    #      @entries = Entry.find(:all)
    #      render_scaffold "list"
    #    end
    #
    #    def show
    #      @entry = Entry.find(params[:id])
    #      render_scaffold
    #    end
    #
    #    def destroy
    #      Entry.find(params[:id]).destroy
    #      redirect_to :action => "list"
    #    end
    #
    #    def new
    #      @entry = Entry.new
    #      render_scaffold
    #    end
    #
    #    def create
    #      @entry = Entry.new(params[:entry])
    #      if @entry.save
    #        flash[:notice] = "Entry was successfully created"
    #        redirect_to :action => "list"
    #      else
    #        render_scaffold('new')
    #      end
    #    end
    #
    #    def edit
    #      @entry = Entry.find(params[:id])
    #      render_scaffold
    #    end
    #
    #    def update
    #      @entry = Entry.find(params[:id])
    #      @entry.attributes = params[:entry]
    #
    #      if @entry.save
    #        flash[:notice] = "Entry was successfully updated"
    #        redirect_to :action => "show", :id => @entry
    #      else
    #        render_scaffold('edit')
    #      end
    #    end
    #  end
    #
    # The <tt>render_scaffold</tt> method will first check to see if you've made your own template (like "weblog/show.rhtml" for
    # the show action) and if not, then render the generic template for that action. This gives you the possibility of using the
    # scaffold while you're building your specific application. Start out with a totally generic setup, then replace one template
    # and one action at a time while relying on the rest of the scaffolded templates and actions.
    module ClassMethods
      # Adds a swath of generic CRUD actions to the controller. The +model_id+ is automatically converted into a class name unless
      # one is specifically provide through <tt>options[:class_name]</tt>. So <tt>scaffold :post</tt> would use Post as the class
      # and @post/@posts for the instance variables.
      #
      # It's possible to use more than one scaffold in a single controller by specifying <tt>options[:suffix] = true</tt>. This will
      # make <tt>scaffold :post, :suffix => true</tt> use method names like list_post, show_post, and create_post
      # instead of just list, show, and post. If suffix is used, then no index method is added.
      def scaffold(model_id, options = {})
        options.assert_valid_keys(:class_name, :suffix)

        singular_name = model_id.to_s
        class_name    = options[:class_name] || singular_name.camelize
        plural_name   = singular_name.pluralize
        suffix        = options[:suffix] ? "_#{singular_name}" : ""

        unless options[:suffix]
          module_eval <<-"end_eval", __FILE__, __LINE__
            def index
              list
            end
          end_eval
        end

        module_eval <<-"end_eval", __FILE__, __LINE__

          verify :method => :post, \:only => [ :destroy#{suffix}, :create#{suffix}, :update#{suffix} ],
                 :redirect_to => { :action => :list#{suffix} }


          def list#{suffix}
            @#{singular_name}_pages, @#{plural_name} = paginate :#{plural_name}, :per_page => 10
            render#{suffix}_scaffold "list#{suffix}"
          end

          def show#{suffix}
            @#{singular_name} = #{class_name}.find(params[:id])
            render#{suffix}_scaffold
          end

          def destroy#{suffix}
            #{class_name}.find(params[:id]).destroy
            redirect_to :action => "list#{suffix}"
          end

          def new#{suffix}
            @#{singular_name} = #{class_name}.new
            render#{suffix}_scaffold
          end

          def create#{suffix}
            @#{singular_name} = #{class_name}.new(params[:#{singular_name}])
            if @#{singular_name}.save
              flash[:notice] = "#{class_name} was successfully created"
              redirect_to :action => "list#{suffix}"
            else
              render#{suffix}_scaffold('new')
            end
          end

          def edit#{suffix}
            @#{singular_name} = #{class_name}.find(params[:id])
            render#{suffix}_scaffold
          end

          def update#{suffix}
            @#{singular_name} = #{class_name}.find(params[:id])
            @#{singular_name}.attributes = params[:#{singular_name}]

            if @#{singular_name}.save
              flash[:notice] = "#{class_name} was successfully updated"
              redirect_to :action => "show#{suffix}", :id => @#{singular_name}
            else
              render#{suffix}_scaffold('edit')
            end
          end

          private
            def render#{suffix}_scaffold(action=nil)
              action ||= caller_method_name(caller)
              # logger.info ("testing template:" + "\#{self.class.controller_path}/\#{action}") if logger

              if template_exists?("\#{self.class.controller_path}/\#{action}")
                render :action => action
              else
                @scaffold_class = #{class_name}
                @scaffold_singular_name, @scaffold_plural_name = "#{singular_name}", "#{plural_name}"
                @scaffold_suffix = "#{suffix}"
                add_instance_variables_to_assigns

                @template.instance_variable_set("@content_for_layout", @template.render_file(scaffold_path(action.sub(/#{suffix}$/, "")), false))

                if !active_layout.nil?
                  render :file => active_layout, :use_full_path => true
                else
                  render :file => scaffold_path('layout')
                end
              end
            end

            def scaffold_path(template_name)
              File.dirname(__FILE__) + "/templates/scaffolds/" + template_name + ".rhtml"
            end

            def caller_method_name(caller)
              caller.first.scan(/`(.*)'/).first.first # ' ruby-mode
            end
        end_eval
      end
    end
  end
end

其中module_eval的方式很不错