private function process(ClassMetadata $metadata, Builder $builder)
 {
     foreach ($metadata->getFieldNames() as $fname) {
         if ($metadata->isIdentifier($fname)) {
             $builder->none($fname);
         } elseif (!$builder->has($fname)) {
             $mapping = $metadata->fieldMappings[$fname];
             $this->makeField($mapping, $builder);
         }
     }
 }