undefined method `items' for nil:NilClass

Hi everybody..

I would appreciate it very much if someone can guide me in the right
direction in solving this problem I have been experiencing.

The problem occurs when I want to add to cart.

I am following the guide in "Agile web development with rails". It was
working before, but then the application needed some AJAX and also two
of the views needed to be converted to partials.

Now I can't get it to work anymore..

It is bound to be some small problem somewhere that I have been blind
to..

It occurs when I try to load the store index page..

********************Error Message***************************

NoMethodError in Store#showmakes

Showing app/views/store/_cart.html.erb where line #3 raised:

undefined method `items' for nil:NilClass

Extracted source (around line #3):

1: <div class="cart_title">Your Cart</div>
2: <table>
3: <%= render(:partial => "cart_item", :collection => cart.items) %>
4:
5: <tr class="total-line">
6: <td colspan="2">Total</td>

Trace of template inclusion: app/views/layouts/cameras.html.erb

*******************store index(Working)************************

<h1>Your Pragmatic Catalog</h1>

<% if @cameras.count > 1 then %>
  <% @cameratypes.each do |camera| -%>
  <% @firstoftype = find_first_image_in_type(camera.camtype)%>
  <%= link_to(image_tag(@firstoftype.image_url), showmakes_url(:id =>
camera.camtype)) %>
  <div>
    <h3><%=h @firstoftype.image_url + ' ' + camera.camtype%></h3>
  </div>
  <% end %>
<% end %>

******************_cart partial*********************

<div class="cart_title">Your Cart</div>
<table>
  <%= render(:partial => "cart_item", :collection => cart.items) %>

  <tr class="total-line">
    <td colspan="2">Total</td>
    <td class="total-cell"><%= number_to_currency(cart.total_price)
%></td>
  </tr>
</table>

<%= button_to 'Empty cart', :action => 'empty_cart' %>

*******************_cart_item partial**************

<tr>
  <td><%= cart_item.quantity %> &times; <%=h cart_item.make %> <%=h
cart_item.model %></td>
  <td class="item-price"><%= number_to_currency(cart_item.price) %></td>
</tr>

*******************add_to_cart.js.rjs***************

page.replace_html("cart", :partial => "cart", :object => @cart)

*******************showmakes view*******************

<h1>Your Pragmatic Catalog</h1>

<% @camerasbytype.each do |camera| -%>
<div>
  <% @firstofmake = find_first_image_in_make(camera.make)%>
  <%= link_to(image_tag(@firstofmake.image_url), showmodels_url(:typeid
=> camera.camtype, :makeid => camera.make)) %>
  <h3><%=h camera.make%></h3>
</div>
<% end %>

********************showmodels view****************

<% @cameramodels.each do |camera| -%>
<div class="entry">
  <fieldset>
    <legend>
    <h3><%= image_tag(camera.image_url) %></h3>
    <h3><%=h camera.model%></h3>
    <h3><%=h camera.description %></h3>
    <div class="price-line">
      <span class="price"><%= number_to_currency(camera.price) %></span>
      <% form_remote_tag :url => {:action => 'add_to_cart', :id =>
camera } do %>
        <%= submit_tag "Add to Cart" %>
      <% end %>
    </div>
    </legend>
  </fieldset>
</div>
<% end %>

*********************store controller**************

class StoreController < ApplicationController

  helper_method :find_first_image_in_type, :find_first_image_in_make

  def index
    @cameras = Camera.find_cameras_for_sale
    @cameratypes = Camera.find_cameras_by_camtype
  end

  def find_first_image_in_type(camtype)
    Camera.find_first_type_image(camtype)
  end

  def find_first_image_in_make(cammake)
    Camera.find_first_make_image(cammake)
  end

  def showmakes
    @camtype = params[:id]
    @camerasbytype = Camera.find_cameras_of_type(@camtype)
  end

  def showmodels
    @camtype = params[:typeid]
    @cammake = params[:makeid]
    @cameramodels = Camera.find_cameras_by_make_and_type(@camtype,
@cammake)
    @cart = find_cart
  end

  def add_to_cart
    camera = Camera.find(params[:id])
    @cart = find_cart
    @cart.add_camera(camera)
    respond_to do |format|
      format.js
    end
    redirect_to_index
  rescue
    logger.error("Attempt to access invalid camera #{params[:id]}")
    redirect_to_index("Invalid camera")
  end

  def empty_cart
    session[:cart] = nil
    redirect_to_index("Your cart is currenty empty")
  end

  private
  def find_cart
    session[:cart] ||= Cart.new
  end

  def redirect_to_index(msg = nil)
    flash[:notice] = msg if msg
    redirect_to :action =>'index'
  end
end

The important line to start at is where the error says:

Showing app/views/store/_cart.html.erb where line #3 raised:
undefined method `items' for nil:NilClass

So you know that on line 3 of that file, you're accessing the .items
method of an object, but that object is actually nil... when you
probably expect it to be an instance of something.

Line 3 says:

3: <%= render(:partial => "cart_item", :collection => cart.items) %>

so we're looking at the "cart.items" - and can safely assume that
"cart" isn't actually a Cart object (or whatever it needs to be), but
is in fact nil. Since this is a partial - you probably have a line in
your index.html.erb file which renders the partial, passing a Cart to
it.

Looking at the controller's index method (that's where you said it was
failing), we can see that there's no definition for the @cart:

def index
@cameras = Camera.find_cameras_for_sale
@cameratypes = Camera.find_cameras_by_camtype
end

So you might benefit from putting a line "@cart = find_cart" in there.
On the flip side (because there's a couple of gaps in the code you
posted), it may be that "cart" in the partial actually needs to be
"@cart".
Try one change first. If it doesn't work, back it out and try the
other. If it still doesn't work, try them both :wink:

Failing that, post back again, and I'll have a look in my copy of the
book to see what it should be...

Very good suggestion Michael.. Thanks for your help.. I have deviated a
little from the book, since there are more functions that I need to
incorporate.. I tried putting it in the index def in the store
controller, but no luck.. Tried putting the @cart.find_cart in the
controller but no luck.. I believe the add_to_cart.js_rjs renders the
cart partial. Don't no why the index would render or look for it..

The add_to_cart function in the store controller is called by a button
on the page 'showmodels'. In the handbook the @cart.find_item is
located in the add_to_cart function