# Railroad problem with :through?

**URL:** <https://discuss.rubyonrails.org/t/railroad-problem-with-through/54721>\
**Category:** rubyonrails-talk\
**Created:** [September 29, 2010, 9:52am UTC](https://discuss.rubyonrails.org/t/railroad-problem-with-through/54721 "2010-09-29T09:52:30Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![11155](https://avatars.discourse-cdn.com/v4/letter/1/d26b3c/32.png) [@11155](https://discuss.rubyonrails.org/u/11155)\
**Post date:** [September 29, 2010, 9:52am UTC](https://discuss.rubyonrails.org/t/railroad-problem-with-through/54721/1 "2010-09-29T09:52:30Z")

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I have the following model layout:

class List \< ActiveRecord::Base has\_many :subscribers, :through =\> :list\_subscribers has\_many :list\_subscribers end

class Subscriber \< ActiveRecord::Base has\_many :lists has\_many :lists, :through =\> :list\_subscribers end

class ListSubscriber\< ActiveRecord::Base belongs\_to :list belongs\_to :subscriber

validates\_uniqueness\_of :subscriber\_id, :scope =\> :list\_id end

and get the following error:

railroad -i -l -a -m -M | dot -Tpng | sed 's/font-size:14.00/font-size:12.00/g' \> doc/models.png /usr/lib/ruby/gems/1.8/gems/activesupport-2.3.8/lib/active\_support/whiny\_nil.rb:52:in `method_missing': undefined method `klass' for nil:NilClass (NoMethodError) from /usr/lib/ruby/gems/1.8/gems/activerecord-2.3.8/lib/active\_record/reflection.rb:320:in `source_reflection' from /usr/lib/ruby/gems/1.8/gems/activerecord-2.3.8/lib/active_record/reflection.rb:320:in `collect' from /usr/lib/ruby/gems/1.8/gems/activerecord-2.3.8/lib/active\_record/reflection.rb:320:in `source_reflection' from /usr/lib/ruby/gems/1.8/gems/activerecord-2.3.8/lib/active_record/reflection.rb:381:in `derive\_class\_name' from /usr/lib/ruby/gems/1.8/gems/activerecord-2.3.8/lib/active\_record/reflection.rb:112:in `class_name' from /home/kaitest/.gem/ruby/1.8/gems/dmattes-railroad_xing-0.5.4/lib/railroad/ar_model.rb:85:in `process\_association' from /home/kaitest/.gem/ruby/1.8/gems/dmattes-railroad\_xing-0.5.4/lib/railroad/ar\_model.rb:65:in `edges' from /home/kaitest/.gem/ruby/1.8/gems/dmattes-railroad_xing-0.5.4/lib/railroad/ar_model.rb:64:in `each' from /home/kaitest/.gem/ruby/1.8/gems/dmattes-railroad\_xing-0.5.4/lib/railroad/ar\_model.rb:64:in `edges' from /home/kaitest/.gem/ruby/1.8/gems/dmattes-railroad_xing-0.5.4/lib/railroad/models_diagram.rb:69:in `process\_class' from /home/kaitest/.gem/ruby/1.8/gems/dmattes-railroad\_xing-0.5.4/lib/railroad/models\_diagram.rb:29:in `generate' from /home/kaitest/.gem/ruby/1.8/gems/dmattes-railroad_xing-0.5.4/lib/railroad/models_diagram.rb:28:in `each' from /home/kaitest/.gem/ruby/1.8/gems/dmattes-railroad\_xing-0.5.4/lib/railroad/models\_diagram.rb:28:in `generate' from /home/kaitest/.gem/ruby/1.8/gems/dmattes-railroad_xing-0.5.4/bin/railroad:47 from /home/kaitest/.gem/ruby/1.8/bin/railroad:19:in `load' from /home/kaitest/.gem/ruby/1.8/bin/railroad:19

Any help much appreciated.

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<div class="post-metadata">

**Author:** ![11155](https://avatars.discourse-cdn.com/v4/letter/1/d26b3c/32.png) [@11155](https://discuss.rubyonrails.org/u/11155)\
**Post date:** [September 29, 2010, 3:05pm UTC](https://discuss.rubyonrails.org/t/railroad-problem-with-through/54721/2 "2010-09-29T15:05:57Z")

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Sem Ptiri wrote:

Is this a typo, or your problem source?

> class Subscriber \< ActiveRecord::Base has\_many :lists has\_many :lists, :through =\> :list\_subscribers end

class Subscriber \< ActiveRecord::Base &nbsp;&nbsp;has\_many :list\_subscribers &nbsp;&nbsp;has\_many :lists, :through =\> :list\_subscribers end

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<div class="post-metadata">

**Author:** ![11155](https://avatars.discourse-cdn.com/v4/letter/1/d26b3c/32.png) [@11155](https://discuss.rubyonrails.org/u/11155)\
**Post date:** [September 30, 2010, 7:42am UTC](https://discuss.rubyonrails.org/t/railroad-problem-with-through/54721/3 "2010-09-30T07:42:40Z")

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Ar Chron wrote:

> Sem Ptiri wrote:
> 
> Is this a typo, or your problem source?
> 
> > class Subscriber \< ActiveRecord::Base has\_many :lists has\_many :lists, :through =\> :list\_subscribers end
> 
> class Subscriber \< ActiveRecord::Base &nbsp;&nbsp;has\_many :list\_subscribers &nbsp;&nbsp;has\_many :lists, :through =\> :list\_subscribers end

My problem source.

Thank you.