Doctrine\ORM\UnitOfWork::getEntityIdentifier PHP Method

    public function getEntityIdentifier($entity)
    {
        return $this->entityIdentifiers[spl_object_hash($entity)];
    }

 /**
  * convert foreign identifiers into scalar foreign key values to avoid object to string conversion failures.
  *
  * @param ClassMetadata $class
  * @param array         $id
  *
  * @return array
  */
 public function flattenIdentifier(ClassMetadata $class, array $id)
 {
     $flatId = array();
     foreach ($class->identifier as $field) {
         if (isset($class->associationMappings[$field]) && isset($id[$field]) && is_object($id[$field])) {
             /* @var $targetClassMetadata ClassMetadata */
             $targetClassMetadata = $this->metadataFactory->getMetadataFor($class->associationMappings[$field]['targetEntity']);
             if ($this->unitOfWork->isInIdentityMap($id[$field])) {
                 $associatedId = $this->flattenIdentifier($targetClassMetadata, $this->unitOfWork->getEntityIdentifier($id[$field]));
             } else {
                 $associatedId = $this->flattenIdentifier($targetClassMetadata, $targetClassMetadata->getIdentifierValues($id[$field]));
             }
             $flatId[$field] = implode(' ', $associatedId);
         } elseif (isset($class->associationMappings[$field])) {
             $associatedId = array();
             foreach ($class->associationMappings[$field]['joinColumns'] as $joinColumn) {
                 $associatedId[] = $id[$joinColumn['name']];
             }
             $flatId[$field] = implode(' ', $associatedId);
         } else {
             $flatId[$field] = $id[$field];
         }
     }
     return $flatId;
 }