title: Checkbox field for nested model
body: <p>I have a form with a nested <code>fields_for</code> form for each person. The idea is the user can select which person to add to the booking using a checkbox</p>
  
  <pre><code>&lt;%= form_for(@booking) do |f| %&gt;    
    &lt;% people.each do |person| %&gt;
      &lt;%= f.fields_for :appointments do |builder| %&gt;
        &lt;p&gt;                                     
          &lt;%= builder.hidden_field :event_id, :value =&gt; @event.id %&gt;  
          &lt;%= builder.check_box :person_id, :value =&gt; person.id %&gt;
        &lt;/p&gt;
      &lt;% end %&gt;
    &lt;% end %&gt;
  &lt;% end %&gt;
  </code></pre>
  
  <p>The trouble is, the checkbox value is always "1" If i replace check_box with text_field, I get all the fields displayed correctly, with the right values, and the form submits through to create the booking. </p>
  
  <p>How can I get the <code>check_box</code> field to display with the <code>person.id</code> not 1 as the value?</p>