Rails - Feb 2006 - no method error - you have a nil object....

hi,

i''ve been cracking my head on this one for a while and would be humbly 
grateful for any pointers

i''m working through Agile Web Devopment w Rails and, in the depot 
example have created the cart class for session handling, but am getting 
the following error, which suggests the @items variable is not being 
populated with any data from LineItem

NoMethodError (You have a nil object when you didn''t expect it!
You might have expected an instance of Array.
The error occured while evaluating nil.<<):
    /app/models/cart.rb:12:in `add_product''
    /app/controllers/store_controller.rb:10:in `add_to_cart''

i''ve triple-checked the code, and found the error in the book through 
the errata, but really am stumped by this error.
any suggestions on good troubleshooting techniques .  i have tried rake 
- which says it can''t connect to mysql through the socket file - even 
though the rest of the db access seems to work fine.   i suspect this is 
part of the problem, seeing as the variable is empty, but don''t know
how
to pin it down .

i''ve also tried  irb store_controller, which seems fine, except for:

NameError: uninitialized constant ApplicationController
        from app/controllers/store_controller.rb:1


code (with my some of my own comments as follows). once again, thanks in 
advance:

class Cart

  attr_reader :items
  attr_reader :total_price

  def initialise
    @items = []
    @total_price = 0.0
  end

  def add_product(product)
    @items << LineItem.for_product(product)  #uses helper class method 
"for_product" in model: line_item.rb, which creates a line_item based
on
a given product
    @total_price += product.price
  end
end
====class StoreController < ApplicationController

  def index  #  calls salable_items function in the controller to create 
a list of items that are available for sale depending on date
    @products = Product.salable_items
  end

  def add_to_cart #  method to add product with :id to the cart with 
redirect to display
    product = Product.find(params[:id])
    @cart = find_cart  # gets existing cart object or creates new one
    @cart.add_product(product)  # add product method sits in the Cart 
class (in models)
    redirect_to(:action => ''display_cart'')
  end

  def display_cart
    @cart = find_cart
    @items = @cart.items
  end

  private   # everything below here is private.  any public actions need 
to be above this part of the class
  def find_cart  # creates a new cart session object if one doesn''t 
exist pg 81
    @cart = session[:cart] ||= Cart.new
  end

end



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