ruby on rails - has_many nested form with a has_one nested form within it -

i trying make form model, has dynamic number of nested models. i'm using nested forms (as described in railscasts 197). make things more complicated, each of nested models has has_one association third model, added form.

for wondering on normalization or improper approach, example simplified version of problem i'm facing. in reality, things more complex, , approach we've decided take.

some example code illustrate problem below:

#models class test    attr_accessible :test_name, :test_description, :questions_attributes   has_many :questions   accepts_nested_attributes_for :questions end  class question   attr_accessible :question, :answer_attributes   belongs_to :test   has_one :answer   accepts_nested_attributes_for :answer end  class answer   attr_accessible :answer   belongs_to :question end  #controller class testscontroller < applicationcontroller    #get /tests/new   def new     @test = test.new     @questions = @test.questions.build     @answers = @questions.build_answer   end  end  #view <%= form_for @test |f| %>   <%= f.label :test_name %>   <%= f.text_box :test_name %>   <%= f.label :test_description %>   <%= f.text_area :test_description %>   <%= f.fields_for :questions |questions_builder| %>     <%= questions_builder.label :question %>     <%= questions_builder.text_box :question %>       <%= questions_builder.fields_for :answer |answers_builder| %>         <%= answers_builder.label :answer %>         <%= answers_builder.text_box :answer %>       <% end %>   <% end %>   <%= link_to_add_fields 'new', f, :questions %> <% end %> 

this code example works first instance of question. issue occurs when question dynamically added created; answer fields not displayed. believe because built first question in controller. there way achieve using nested_attributes?

i solved own issue here. did was, instead of building answer model in controller (which impossible when not know how many questions going made in view), built when calling fields_for:

#controller class testscontroller < applicationcontroller    #get /tests/new   def new     @test = test.new     @questions = @test.questions.build   end  end  #view <%= form_for @test |f| %>   <%= f.label :test_name %>   <%= f.text_box :test_name %>   <%= f.label :test_description %>   <%= f.text_area :test_description %>   <%= f.fields_for :questions |questions_builder| %>     <%= questions_builder.label :question %>     <%= questions_builder.text_box :question %>     <%= questions_builder.fields_for :answer, @questions.build_answer |answers_builder| %>       <%= answers_builder.label :answer %>       <%= answers_builder.text_box :answer %>     <% end %>   <% end %>   <%= link_to_add_fields 'new', f, :questions %> <% end %> 

this works because no matter how many question forms being built on view, new answer specific question being built built.