# parameters that are being sent:

  Processing by ExamTemplatesController#create as HTML
  Parameters: {"commit"=>"Create Exam Template", "authenticity_token"=>"XGTV17fAkOxLt4Z8Of4BNXBbh3iAILxhMJFKTL1yVBw=", "utf8"=>"\342\234\223", "exam_sheet_template"=>{"category_id"=>"2"}, "exam_template"=>{"name"=>"test", "exam_sheet_template_attributes"=>{"0"=>{"amount"=>"2", "_destroy"=>"0"}, "1"=>{"amount"=>"2", "_destroy"=>"0"}, "2"=>{"amount"=>"2", "_destroy"=>"0"}}}}

# as you can see, "exam_sheet_template"=>{"category_id"=>"2"}" is set only once, outside the exam_sheet_template attributes section, where i expect it.

<p>
  <%= collection_select(:exam_sheet_template, :category_id, Category.all, "id", "category_name") %>
  <%= f.text_field :amount, :size => 2 %>
  <%= f.check_box :_destroy %>
  <%= f.label :_destroy, "Remove Exam Sheet" %><br/>
</p>