ruby on rails - How to create association for nested model in a form -

in ruby on rails application want allow adding/editing of nested model has associated model.

model survey    string title    has_many questions  model question    string question    belongs_to category  model category    string name 

for sake of argument let's assume user should have enter new category when entering question (i couldn't come better example, sigh).

in model/survey/edit.html.erb have working setup adding questions , saving them. when added category model picture, face problem when adding new question, there no corresponding category name-field displayed. suspect because though call question.new, not call question.category.build - , have no idea where/how that.

my edit.html.erb:

<h1>editing survey</h1>  <%= render :partial => 'form' %> 

my _form.html.erb:

<% form_for(@survey) |f| %>   <%= f.error_messages %>    <p>     <%= f.label :title %><br />     <%= f.text_field :title %>   </p>    <div id="questions">     <% f.fields_for :questions |q| %>       <%= render :partial => 'question', :locals => { :pf => q } %>     <% end %>   </div>    <%= add_a_new_child_link("new question", f, :questions) %> <% end %> 

my _question.html.erb:

<div class="question">   <%= pf.label :question %>   <%= pf.text_field :question %>    <% pf.fields_for :category |c| %>     <p>       <%= c.label :name, "category:" %>       <%= c.text_field :name %>     </p>   <% end %> </div> 

a quick fix situation use virtual attributes. eg, in question model:

def category_name=(new_name)  if category    category.name = new_name  else    category = category.new(:name => new_name)  end end  def category_name   return category.name if category    "" end 

in _question, there no need use nested form. add like:

<%= pf.text_field :category_name %> 

i didn't test it, caught ideea.