private function getIdentifierField()
{
if (null !== $this->identifierField) {
return $this->identifierField;
}
$metadata = $this->em->getClassMetadata($this->table->getEntity());
if ($metadata->isIdentifierComposite) {
throw new \Exception('composite identifiers are currently not supported.');
}
$identifier = $metadata->getIdentifier();
if (1 !== sizeof($identifier)) {
throw new \Exception('exactly one identifier expected.');
}
$this->identifierField = $identifier[0];
return $this->identifierField;
}