In content type there are three field . Each field are node reference to different content. Here I want to restrict value and create dependency on these field. For example: I have one auto complete field “Country”. On change of “Country”, select list(i.e. State) field value is updated. On change of “State”, “county” field is updated. Everything is working fine.

When I change value of “Country”, “State” value get change But “county” value hold previous value. How should I achieve this. How should I reset value of county

My code snippet is like

function module_form_alter(&$form, &$form_state, $form_id) {   $form['field_country'][LANGUAGE_NONE]['#ajax'] = array(     'callback' => '_state_list_callback',     'event'    => 'change',     'wrapper' => 'state-list',     'progress' => array('type' => 'throbber', 'message' =>  'Please wait...'), );   $form['field_country']['#prefix'] = '<div id="state-list">';   $form['field_country']['#suffix'] = '</div>';    $form['field_state'][LANGUAGE_NONE]['#ajax'] = array(     'callback' => '_county_list_callback',     'event'    => 'change',     'wrapper' => 'county-list',     'progress' => array('type' => 'throbber', 'message' =>  'Please wait...'), );   $form['field_county']['#prefix'] = '<div id="county-list">';   $form['field_county']['#suffix'] = '</div>'; }   function _county_list_callback(&$form, &$form_state) {   return $form['field_county']; }  function _state_list_callback(&$form, &$form_state) {   return $form['field_state']; }