.collect on a belongs_to raising NoMethodError: undefined method `add' for nil:NilClass

Question

Setup: Rails 3 RC2, Ruby 1.9.2 p0 (also tried on Rails 3 beta 4, Ruby 1.8.7 p174)

I have quite a basic shopping cart setup:

Order has_many :order_items
Order has_many :products, :through => :order_items, :dependent => :restrict

Product has_many :order_items
Product has_many :orders, :through => :order_items, :dependent => :restrict

OrderItem belongs_to :product
OrderItem belongs_to :order

After creating Products and OrderItems I head into the console and try the following:

Order.last.order_items.collect { |item| { :name => item.product.name, :quantity => item.quantity } }

And I get an error:

NoMethodError: undefined method `add' for nil:NilClass
    from /Users/tcoop/.rvm/gems/ruby-1.9.2-p0/gems/activesupport-3.0.0.rc2/lib/active_support/whiny_nil.rb:48:in `method_missing'
    from /Users/tcoop/.rvm/gems/ruby-1.9.2-p0/gems/bullet-2.0.0.rc1/lib/bullet/detector/n_plus_one_query.rb:21:in `create_notification'
    from /Users/tcoop/.rvm/gems/ruby-1.9.2-p0/gems/bullet-2.0.0.rc1/lib/bullet/detector/n_plus_one_query.rb:14:in `call_association'
    from /Users/tcoop/.rvm/gems/ruby-1.9.2-p0/gems/bullet-2.0.0.rc1/lib/bullet/active_record3.rb:78:in `load_target'
    from /Users/tcoop/.rvm/gems/ruby-1.9.2-p0/gems/activerecord-3.0.0.rc2/lib/active_record/associations/association_proxy.rb:118:in `reload'
    from /Users/tcoop/.rvm/gems/ruby-1.9.2-p0/gems/activerecord-3.0.0.rc2/lib/active_record/associations.rb:1451:in `block in association_accessor_methods'
    from (irb):6:in `block in irb_binding'
    from /Users/tcoop/.rvm/gems/ruby-1.9.2-p0/gems/activerecord-3.0.0.rc2/lib/active_record/associations/association_collection.rb:430:in `block in method_missing'
    from /Users/tcoop/.rvm/gems/ruby-1.9.2-p0/gems/activerecord-3.0.0.rc2/lib/active_record/associations/association_proxy.rb:216:in `block in method_missing'
    from /Users/tcoop/.rvm/gems/ruby-1.9.2-p0/gems/activerecord-3.0.0.rc2/lib/active_record/associations/association_proxy.rb:216:in `collect'
    from /Users/tcoop/.rvm/gems/ruby-1.9.2-p0/gems/activerecord-3.0.0.rc2/lib/active_record/associations/association_proxy.rb:216:in `method_missing'
    from /Users/tcoop/.rvm/gems/ruby-1.9.2-p0/gems/activerecord-3.0.0.rc2/lib/active_record/associations/association_collection.rb:430:in `method_missing'
    from (irb):6
    from /Users/tcoop/.rvm/gems/ruby-1.9.2-p0/gems/railties-3.0.0.rc2/lib/rails/commands/console.rb:44:in `start'
    from /Users/tcoop/.rvm/gems/ruby-1.9.2-p0/gems/railties-3.0.0.rc2/lib/rails/commands/console.rb:8:in `start'
    from /Users/tcoop/.rvm/gems/ruby-1.9.2-p0/gems/railties-3.0.0.rc2/lib/rails/commands.rb:23:in `<top (required)>'
    from script/rails:6:in `require'
    from script/rails:6:in `<main>'

I know the products do exist AND that the order_item is valid... If I do the following:

ruby-1.9.2-p0 > Order.last.order_items.collect { |item| { :name => item.product_id, :quantity => item.quantity } }

Then I get what I was expecting: => [{:name=>3, :quantity=>1}, {:name=>1, :quantity=>4}]

I am not sure why calling an attribute on the associated object (item.product.name) is raising errors - can anyone shed some light on this for me please?

EDIT I just added the following as a comment but the formatting is horrible...

I also forgot to mention that this only happens with there are more than 1 order_items. 1 order item works as expected. AND the following seems to solve my problem...

products = order.order_items.collect do |item|
  uid = item.product.uid
  { :ProductUID => uid, :Quantity => item.quantity }
end

Thanks

Answer 1

This is wrong at least (or you made a typo)

Product has_many :order, :through => :order_items, :dependent => :restrict
                       |
                       V
Product has_many :orders, :through => :order_items, :dependent => :restrict

Hard to say if it's complaining about that with all those method missing flying around but correct that at least. Cheers.

Answer 2

It seems that the bullet gem (currently in RC) was causing the problem. I found this issue (http://github.com/flyerhzm/bullet/issues/#issue/31) on the bullet github page. I have left my information there for the owner to look into.

Answer 3

Sorry for the delay, I guess the issue should be solved if you upgrade your bullet gem to 2.0.0.rc2