knowledge.rb

 class Knowledge < ActiveRecord::Base
        has_one :knowledge_file, :dependent => :destroy
        attr_accessible :problem, :solution, :knowledge_file_attributes
   accepts_nested_attributes_for :knowledge_file

knowledge_file.rb

class KnowledgeFile < ActiveRecord::Base
	belongs_to :knowledge
end

knowledge_files_controller.rb

class KnowledgeFilesController < ApplicationController
	layout 'application'

	def create
		uploaded_io = params[:knowledge_file][:name]
	  @knowledge_file = KnowledgeFile.new(params[:knowledge_file])
		@knowledge_file.knowledge_id = params[:knowledge_id]
		@knowledge_file.update_attribute("name", uploaded_io.original_filename)
		File.open(Rails.root.to_s + '/public/uploads/' + params[:knowledge_id] + "-" + uploaded_io.original_filename, 'wb') do |file|
			file.write(uploaded_io.read)
			redirect_to :back
		end
	end

	def destroy
		@knowledge_file = KnowledgeFile.find(params[:id])
		@knowledge = @knowledge_file.knowledge_id
		
		if File.exist?("#{Rails.root}/public/uploads/#{@knowledge_file.name}")
			File.delete("#{Rails.root}/public/uploads/#{@knowledge_file.name}")
			redirect_to :back
		else
			flash[:notice] = "The file has been deleted"
		end
		@knowledge_file.destroy
	end

	def upload
		uploaded_io = params[:knowledge_file][:name]
	  @knowledge_file = KnowledgeFile.new(params[:knowledge_file])
		@knowledge_file.knowledge_id = params[:knowledge_id]
		@knowledge_file.update_attribute("name", uploaded_io.original_filename)
		File.open(Rails.root + '/public/uploads/' + uploaded_io.original_filename, 'w') do |file|
			file.write(uploaded_io.read)
			redirect_to :back
		end
 end

	def download
		file = KnowledgeFile.find(params[:id])
		send_file Rails.root + '/public/uploads/' + file.name
	end 
		

		
end

knowledges_controller.rb

class KnowledgesController < ApplicationController

	def index
		if params[:q].present?
			@knowledges = Knowledge.search(params[:q])
		else
			@knowledges = Knowledge.all
		end
		respond_to do |format|
			format.html
		end
	end

	def new
		@knowledge = Knowledge.new
		@knowledge_file = KnowledgeFile.new
		respond_to do |format|
			format.html
		end
	end

	def show
		@knowledge = Knowledge.find(params[:id])
		@files = KnowledgeFile.find_all_by_knowledge_id(@knowledge) 
	respond_to do |format|
			format.html
		end
	
	end

	def create
		@knowledge = Knowledge.new(params[:knowledge])
		if @knowledge.save
			redirect_to knowledges_path 
		else
			redirect_to new_knowledge_path
		end
	end

	def update
		@knowledge = Knowledge.find(params[:id])
		@knowledge.update_attribute(params[:knowledge])
		respond_to do |format| 
			if @knowledge.save
				format.html { redirect_to knowledges_path }
			else
				format.html { render :action => "edit" }
			end
		end
	end

	def edit
		@knowledge = Knowledge.find(params[:id])
		respond_to do |format|
			format.html
		end
	end

	def destroy
		@knowledge = Knowledge.find(params[:id])
		@knowledge.destroy
		redirect_to knowledges_path
	end

	def search
		if params[:q].present?
			@knowledges = Knowledge.search(params[:q])
		else
			@knowledges = Knowledge.all
		end
		respond_to do |format|
			format.html { redirect_to :action => "index" }
		end
	end

end

my_view.html.erb

<%= form_for @knowledge do |knowledge_form| %>

	<%= knowledge_form.label("Problem") %><br />
	<%= knowledge_form.text_area(:problem, :size => "84x6") %><br />
	<%= knowledge_form.label("Solution") %><br />
	<%= knowledge_form.text_area(:solution, :size => "84x6") %><br />

	<%= knowledge_form.fields_for :knowledge_files, :multipart => true do |knowledge_files_form| %>
		<%= knowledge_files_form.label("File") %>
		<%= knowledge_files_form.file_field :name %>
		<%= knowledge_files_form.text_field :description %>
  <% end %>

	<%= knowledge_form.submit "Save" %> 
<% end %>