public function needSourceIndex()
 {
     if ($this->indexes !== null) {
         return;
     }
     $state = new coopy_TableComparisonState();
     $state->a = $this->source;
     $state->b = $this->source;
     $comp = new coopy_CompareTable($state);
     $comp->storeIndexes();
     $comp->run();
     $comp->align();
     $this->indexes = $comp->getIndexes();
     $this->needSourceColumns();
 }