Rails - Sep 2006 - Undefined method "xxx" of a model when calling a helper

Hi all

I''m creating a shop page. I have a cart model that looks like the 
following:

class Cart
  attr_reader :line_items

  def get_line_item id
    @line_items.each do |l|
      return l if l.id == id
    end
  end

  def initialize
    @line_items = []
  end

  def empty!
    initialize
  end

  def empty?
    return true if @line_items.empty?
    false
  end
end

And I have some helper methods in application_helper.rb:

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

  def empty_cart
    find_cart.empty!
  end

  def cart_empty?
    return true if find_cart.empty?
  end
end

Then I want to display a partial form within the layout 
application.rhtml but only if the cart is not empty:

<%= render(:partial => ''warenkorb/warenkorb'', :locals
=> {:cart =>
find_cart}) unless cart_empty? %>

But this displays me the following error:

undefined method `empty?'' for #<Cart:0x230020c @line_items=[]>

Where does this error come from? I just don''t get it, the Cart object
is
instantiated when calling find_cart, and the Cart class definitely does 
have a method called "empty?"!

Thanks for help,
Joshua

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Hi --

On Sun, 3 Sep 2006, Joshua Muheim wrote:
>
> Hi all
>
> I''m creating a shop page. I have a cart model that looks like the
> following:
>
> class Cart
>  attr_reader :line_items
>
>  def get_line_item id
>    @line_items.each do |l|
>      return l if l.id == id
>    end
>  end
    def get_line_item(id)
      @line_items.find {|l| l.id == id }
    end
>  def initialize
>    @line_items = []
>  end
>
>  def empty!
>    initialize
>  end
>
>  def empty?
>    return true if @line_items.empty?
>    false
>  end
    def empty?
      @line_items.empty?
    end
> end
>
> And I have some helper methods in application_helper.rb:
>
> module ApplicationHelper
>  def find_cart
>    session[:cart] ||= Cart.new
It seems a little odd to me to be manipulating the session data in a
view (or view helper).  You might want to find a way to juggle things
so that this is back in the controller.
>  end
>
>  def empty_cart
>    find_cart.empty!
>  end
>
>  def cart_empty?
>    return true if find_cart.empty?
>  end
    def cart_empty?
      find_cart.empty?
    end
> end
>
> Then I want to display a partial form within the layout
> application.rhtml but only if the cart is not empty:
>
> <%= render(:partial => ''warenkorb/warenkorb'',
:locals => {:cart =>
> find_cart}) unless cart_empty? %>
>
> But this displays me the following error:
>
> undefined method `empty?'' for #<Cart:0x230020c
@line_items=[]>
>
> Where does this error come from? I just don''t get it, the Cart
object is
> instantiated when calling find_cart, and the Cart class definitely does
> have a method called "empty?"!
I''m afraid I can''t duplicate your error.  I''ve tried
to make up for it
with a few code hints :-)  (see above)  Could the problem have
something to do with caching and then changing the model file?


David

-- 
                   David A. Black |
dblack-TKXtfPMJ4Ozk1uMJSBkQmQ@public.gmane.org
Author of "Ruby for Rails"   [1] | Ruby/Rails training &
consultancy [3]
DABlog (DAB''s Weblog)        [2] | Co-director, Ruby Central, Inc.  
[4]
[1] http://www.manning.com/black | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com    | [4] http://www.rubycentral.org

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Joshua Muheim wrote:
> class Cart
>   ...
>   def empty?
>     return true if @line_items.empty?
>     false
>   end
> end
> 
> And I have some helper methods in application_helper.rb:
> 
> module ApplicationHelper
>   def cart_empty?
>     return true if find_cart.empty?
>   end
> end
Not sure why you''re getting that error.  Are you sure you dont have a 
nother file redefing the cart class somewhere?  It''s coming from 
"find_cart.empty?" in your helper method.

Also, I''m not sure if this will help, but those methods could a whole 
lot simpler.  in your empty? method, @line_items.empty? already returns 
true or false so it can be greatly simplified to:

  def empty?
    @line_items.empty?
  end

And the same with your cart_empty? helper.  But why use a helper for 
that when you can ask the cart directly if its empty?  It''s less code 
and easier to troubleshoot.

  <%= render :partial ... unless find_cart.empty? %>

Lastly, do all the other method on your cart object work ok?

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