public function getColumnValue($model, $column)
 {
     if ($column == 'classID') {
         $mapper = Orm::getMapper($model);
         $primaryKey = $mapper->getAdapter()->getPrimaryKey();
         return $model->{$primaryKey};
     }
     return parent::getColumnValue($model, $column);
 }
 public function getSourceMapper()
 {
     if (!$this->sourceMapper) {
         $source = $this->getSource();
         if (!$source) {
             throw new \Exception('Unable to load source mapper as no source exists');
         }
         $this->sourceMapper = Orm::getMapper(get_class($source));
     }
     return $this->sourceMapper;
 }