buy book from system user based

hi i'm very new to ROR. i must do a basic library system its my homework. i have models, user.rb (created by restful_authentication plugin) and book.rb (created by scaffolding) controllers: sessions_controller and users_controller(created by restful_authentication plugin) and books_controller(created by scaffolding)

****user.rb,sessions_controller,users controller have the same codes restful_authentication screencast and its working correct**********

and i want to have a buy link at books page for example i login as 'Jack' when i login i'm showing the books page its OK. but also i wanna see buy link and when i click it and return to the books page i wanna see the books Jack bought then logut and login again as'michael ' i wanna see books page and idont wanna see jack's book i just wanna see michael's book how can i do it? here is my books_controller.rb i wanna have an buy action here(user will buy a book)

class BooksController < ApplicationController   # GET /books   # GET /books.xml   def index     @books = Book.all

    respond_to do |format|       format.html # index.html.erb       format.xml { render :xml => @books }     end   end   # GET /books/1   # GET /books/1.xml   def show

    @book = Book.find(params[:id])     respond_to do |format|       format.html # show.html.erb       format.xml { render :xml => @book }     end   end   # GET /books/new   # GET /books/new.xml   def new     @book = Book.new     respond_to do |format|       format.html # new.html.erb       format.xml { render :xml => @book }     end   end   # GET /books/1/edit   def edit     @book = Book.find(params[:id])   end   # POST /books   # POST /books.xml   def create     @book = Book.new(params[:book])     respond_to do |format|       if @book.save         flash[:notice] = 'Book was successfully created.'         format.html { redirect_to(@book) }         format.xml { render :xml => @book, :status => :created, :location => @book }       else         format.html { render :action => "new" }         format.xml { render :xml => @book.errors, :status => :unprocessable_entity }       end     end   end   # PUT /books/1   # PUT /books/1.xml   def update     @book = Book.find(params[:id])     respond_to do |format|       if @book.update_attributes(params[:book])         flash[:notice] = 'Book was successfully updated.'         format.html { redirect_to(@book) }         format.xml { head :ok }       else         format.html { render :action => "edit" }         format.xml { render :xml => @book.errors, :status => :unprocessable_entity }       end     end   end   # DELETE /books/1   # DELETE /books/1.xml   def destroy     @book = Book.find(params[:id])     @book.destroy     respond_to do |format|       format.html { redirect_to(books_url) }       format.xml { head :ok }     end   end end and here is my index.html.erb i wanna see buy link and also see which book user bought

<<strong>Welcome <%=current_user.login %> </strong>><%= link_to "logout", logout_path %> <h1>Listing books</h1> <table>   <tr>     <th>Name</th>   </tr> <% @books.each do |book| %>   <tr>     <td><%=h book.name %></td>

    <td><%= link_to 'Show', book %></td>     <td><%= link_to 'Edit', edit_book_path(book) %></td>     <td><%= link_to 'Destroy', book, :confirm => 'Are you sure?', :method => :delete %></td>   </tr> <% end %> </table> <br /> <%= link_to 'New book', new_book_path %> can anyone help? thanks