title: Rails 2.3 nested attributes issue
body: <p>I'm running into to a issue with a nested form which I'm sure should be easily solved, yet I can't find a way around it</p>
  
  <p>Basically I have the following relationship</p>
  
  <pre><code>event has_many :contacts =&gt; through :event_contacts
  </code></pre>
  
  <p>the nested form works perfectly as long as I'm creating new contacts each time. </p>
  
  <p>If I include a drop down to allow selection of an existing contact within the nested form, an event is created, however the contact_id is nil in the event_contacts table.</p>
  
  <p>No contact is created, since I post an 'id' field for the nested contact.. (ie .new_record? returns false.)</p>
  
  <p>So how do I update the event_contacts table to ensure that the 'selected' contacts is properly associated?</p>
  
  <p>See snipbits below...</p>
  
  <p><strong>Models</strong></p>
  
  <pre><code>class Event &lt; ActiveRecord::Base
    belongs_to  :user
  
    has_many    :event_contacts
    accepts_nested_attributes_for :event_contacts 
  
    has_many    :contacts, :through =&gt; :event_contacts
    accepts_nested_attributes_for :contacts
  
  
  class EventContact &lt; ActiveRecord::Base
    belongs_to :event
    belongs_to :contact
  
    accepts_nested_attributes_for :contact
  
  
  class Contact &lt; ActiveRecord::Base
    belongs_to  :user
  
    has_many    :event _contacts
    has_many    :events, :through =&gt; :event_contacts
  </code></pre>
  
  <p><strong>View</strong></p>
  
  <pre><code>- fields_for(@event) do |f|
    - f.fields_for :event_contacts do |rc|
      - rc.fields_for :contact do |c|
        = c.collection_select :id, Contact.all, :id, :name, { :selected =&gt; @contact.id || 0 }
  
        = c.hidden_field :user_id, :value =&gt; @current_user.id 
        = c.text_field :first_name
            = c.text_field :email
  </code></pre>