You have a nil object when you didn't expect it!

rubyonrails-talk
1

I get the following:

NoMethodError in Shoppingcart#my_shopping_cart

Showing app/views/shoppingcart/my_shopping_cart.rhtml where line #33 raised:

You have a nil object when you didn't expect it! The error occurred while evaluating nil.shopping_cart_items

The line in question is

<% for shopping_cart_item in @shopping_cart.shopping_cart_items %>

Any suggestions?

2

I get the following:

NoMethodError in Shoppingcart#my_shopping_cart

Showing app/views/shoppingcart/my_shopping_cart.rhtml where line #33 raised:

You have a nil object when you didn't expect it! The error occurred while evaluating nil.shopping_cart_items

The line in question is

<% for shopping_cart_item in @shopping_cart.shopping_cart_items %>

Any suggestions?

@shopping_cart is nil. You'll need to look at the my_shopping_cart action of the Shoppingcart controller to figure out why that's not being set correctly.

3

Thanks Philip. I'm new here, can you advise on what I need to do prior to get @shopping_cart set? I'm not sure of the exact steps involved in accessing the data in ROR.

4

Here's what I now have, not sure where to go from here:

NameError in Shoppingcart#my_shopping_cart

Showing app/views/shoppingcart/my_shopping_cart.rhtml where line #24 raised:

undefined local variable or method `shopping_cart_item' for Shopping_cart:Class Extracted source (around line #24):

21: <td valign="top" width="50%"></b>Traded items: </b><br> 22: <table> 23: <% if @my_cart 24: for shopping_cart_item in @my_cart.shopping_cart_items %> 25: <tr> 26: <t

5

What does your Shopping_cart class look like? How is shopping_cart_items defined?

6

class Shopping_cart < ActiveRecord::Base   belongs_to :owner,     :class_name => "user",     :foreign_key => "owner_id"

  has_many :shopping_cart_items,     :class_name => "shopping_cart_item",     :finder_sql => "select ti.* from shopping_cart_items ti, shopping_carts t         where ti.owner_id = t.owner_id" end

7

Your shopping_cart_item (singular) is probably a rails model and it needs to start with a capital letter as it should be a ruby constant.

When you define a model or any class in the normal way, you do something like this   class ShoppingCartItem < ActiveRecord::Base   ... ShoppingCartItem is a ruby constant because it starts with capital (as opposed to local variable or method name). Also, you should probably use camel case instead of underscores for constant names - that seems to be a convention but with rails it might be a requirement (not completely sure as I've never done it that way). You'd then refer to this class using class_name => 'ShoppingCartItem' . Your underlying table can stay as shopping_cart_items, of course.

You could probably dispense with class_name altogether if "has_many :shopping_cart_items" refers to model ShoppingCartItem. Rails will infer that for you.

8

Daniel,

thank you so much, now I have the message

NameError in Shoppingcart#my_shopping_cart

Showing app/views/shoppingcart/my_shopping_cart.rhtml where line #25 raised:

uninitialized constant Shopping_cart::ShoppingCartItems Extracted source (around line #25):

23: <% if @my_cart 24: 25: for shopping_cart_item in @my_cart_items.shopping_cart_items %> 26: <tr>

My shoppingcart.rb is

class Shopping_cart < ActiveRecord::Base   belongs_to :owner,     :class_name => "user",     :foreign_key => "owner_id"

  has_many :shopping_cart_items,     :class_name => "ShoppingCartItems",     :finder_sql => "select ti.* from shopping_cart_items ti, shopping_carts t where ti.owner_id = t.owner_id" end

and my shoppingcartitem.rb defines

class ShoppingCartItem

I feel like I'm close, but I can't figure this out. Can you figure out the missing link?

9

You can name your files like: shopping_cart_item.rb but define the class inside as 'ShoppingCartItem'. Similarly for shopping_cart.rb and class ShoppingCart. Glad it helped.