code: protected function loadMetadata($className)
      {
          if (false === isset($this->loadedMetadata[$className])) {
              if (null === ($class = $this->driver->loadMetadataForClass($className))) {
                  // FIXXME Improve this
                  throw new \Exception("Can't load metadata for $className");
              }
  
              $this->completeMetadata($class);
              $this->loadedMetadata[$className] = $class;
          }
  
          return $this->loadedMetadata[$className];
      }
docs: Loads the metadata of the specified class
  
  @param string $nameName The name of the class for which the metadata
  should be loaded.
  
  @return ClassMetadata