/**
  * @param Configuration $config
  * @param EventManager $evm
  */
 public function __construct(Configuration $config = null, EventManager $evm = null)
 {
     $this->configuration = $config ?: new Configuration();
     $this->eventManager = $evm ?: new EventManager();
     $classMetadataFactoryClass = $this->configuration->getClassMetadataFactoryName();
     $this->classMetadataFactory = new $classMetadataFactoryClass($this);
     $this->unitOfWork = new UnitOfWork($this);
 }