Ruby Forum Ruby on Rails > Hitting unknown error with "can't dup NilClass"

Hi,

My system has been encounter this problem, and I couldn't find
solution after debugging. My scenario is stated below:

class user
   has_many :posts
   has_many :comments
end

class post
  belongs_to :user
  has_many :comments, :as => :commentable
end

class comment
  belongs_to :post
  belongs_to :user
end

For this case, I am trying to retrieve each post's comment together
with submitter username and I write as below:

class PostsController<ApplicationController
  def show
      raise @post.comments.first.user.inspect
  end
end

While the first time I run this script, it works fine. But, after I
hitting a refresh, it hits following problem "can't dup NilClass". It
is repeats the same for everytime i restart mongrel, working for the
first time and failed for the rest.

I append the application error log as below:
/opt/local/lib/ruby/gems/1.8/gems/activerecord-2.3.2/lib/active_record/
base.rb:2189:in `dup'
/opt/local/lib/ruby/gems/1.8/gems/activerecord-2.3.2/lib/active_record/
base.rb:2189:in `scoped_methods'
/opt/local/lib/ruby/gems/1.8/gems/activerecord-2.3.2/lib/active_record/
base.rb:2193:in `current_scoped_methods'
/opt/local/lib/ruby/gems/1.8/gems/activerecord-2.3.2/lib/active_record/
base.rb:2183:in `scope'
/opt/local/lib/ruby/gems/1.8/gems/activerecord-2.3.2/lib/active_record/
base.rb:1548:in `find_every'
/opt/local/lib/ruby/gems/1.8/gems/activerecord-2.3.2/lib/active_record/
base.rb:1588:in `find_one'
/opt/local/lib/ruby/gems/1.8/gems/activerecord-2.3.2/lib/active_record/
base.rb:1574:in `find_from_ids'
/opt/local/lib/ruby/gems/1.8/gems/activerecord-2.3.2/lib/active_record/
base.rb:616:in `find'
/opt/local/lib/ruby/gems/1.8/gems/activerecord-2.3.2/lib/active_record/
associations/belongs_to_association.rb:44:in `find_target'
/opt/local/lib/ruby/gems/1.8/gems/activerecord-2.3.2/lib/active_record/
associations/association_proxy.rb:240:in `load_target'
/opt/local/lib/ruby/gems/1.8/gems/activerecord-2.3.2/lib/active_record/
associations/association_proxy.rb:112:in `reload'
/opt/local/lib/ruby/gems/1.8/gems/activerecord-2.3.2/lib/active_record/
associations.rb:1231:in `user'

Need some help for this. Thanks in advance.

Found solution - Use "unloadable" for these classes - 
http://strd6.com/?p=250

I've such problem. First time it works fine. But next time it gets
error "can't dup NilClass"

Yeah, I'm getting the same thing for all associations on one of my 
classes. have you found a solution?