public function get_dropdown($name_field, $null_option = true, $label_function = false, $optgroups = false, $optgroup_constant_prefix = null, $null_value = null, $order_by = null, $where = null)
 {
     $this->db->order_by('name');
     return parent::get_dropdown($name_field, $null_option, $label_function, $optgroups, $optgroup_constant_prefix = null, $null_value, $order_by, $where);
 }
 public function get_dropdown_full_name($null_option = true, $label_function = false, $optgroups = false, $optgroup_constant_prefix = null, $null_value = null, $order_by = null, $where = null)
 {
     $dropdown = parent::get_dropdown('first_name', $null_option, $label_function, $optgroups, $optgroup_constant_prefix, $null_value, $order_by, $where);
     foreach ($dropdown as $user_id => $name) {
         $dropdown[$user_id] = $this->get_name($user_id);
     }
     return $dropdown;
 }