/**
  * Gets the table which contains the sort field.
  *
  * @param DataList $list
  * @return string
  */
 public function getSortTable(SS_List $list)
 {
     $field = $this->getSortField();
     if ($list instanceof ManyManyList) {
         $extra = $list->getExtraFields();
         $table = $list->getJoinTable();
         if ($extra && array_key_exists($field, $extra)) {
             return $table;
         }
     }
     $classes = ClassInfo::dataClassesFor($list->dataClass());
     foreach ($classes as $class) {
         if (singleton($class)->hasOwnTableDatabaseField($field)) {
             return $class;
         }
     }
     throw new Exception("Couldn't find the sort field '{$field}'");
 }