title: Rails - set a db field to null from another object's controller
body: <p>I am attempting to set a Cabinet's Device's attributes to null in a disconnect method.  cabinets_controller calls <code>@cabinet.devices.destroy(@device)</code> and that works ok.  Before I do that I want to set <code>@device.row_id = nil</code> and <code>@device.position = nil</code>.  They are both Fixnum and attr_accesible in the Device model.  They are not being altered in the DB when I call this method.  Is there a method to call on <code>@device</code> to make this happen?</p>
  
  <p>Thanks.</p>