public function registerEntityManager(ApplicationInterface $application, PersistenceUnitNodeInterface $persistenceUnitNode)
{
// initialize the the entity manager instance
$this->entityManagers[$lookupName = $persistenceUnitNode->getName()] = $persistenceUnitNode;
// bind the callback for the entity manager instance to the
// naming directory => necessary for DI provider
$application->getNamingDirectory()->bind(sprintf('php:global/%s/%s', $application->getUniqueName(), $lookupName), array(&$this, 'lookup'), array($lookupName));
}