Neos\Flow\Reflection\ClassSchema::markAsIdentityProperty PHP Method

    public function markAsIdentityProperty($propertyName)
    {
        if ($this->modelType === self::MODELTYPE_VALUEOBJECT) {
            throw new Exception\ClassSchemaConstraintViolationException('Value objects must not have identity properties', 1264102084);
        }
        if (!array_key_exists($propertyName, $this->properties)) {
            throw new \InvalidArgumentException('Property "' . $propertyName . '" must be added to the class schema before it can be marked as identity property.', 1233775407);
        }
        if ($this->properties[$propertyName]['lazy'] === true) {
            throw new \InvalidArgumentException('Property "' . $propertyName . '" must not be marked for lazy loading to be marked as identity property.', 1239896904);
        }
        $this->identityProperties[$propertyName] = $this->properties[$propertyName]['type'];
    }

 /**
  * @param ClassSchema $classSchema
  * @param string $propertyName
  * @return boolean
  * @throws InvalidPropertyTypeException
  * @throws \InvalidArgumentException
  */
 protected function evaluateClassPropertyAnnotationsForSchema(ClassSchema $classSchema, $propertyName)
 {
     $skipArtificialIdentity = false;
     $className = $classSchema->getClassName();
     if ($this->isPropertyAnnotatedWith($className, $propertyName, Flow\Transient::class)) {
         return false;
     }
     if ($this->isPropertyAnnotatedWith($className, $propertyName, Flow\Inject::class)) {
         return false;
     }
     if (!$this->isPropertyTaggedWith($className, $propertyName, 'var')) {
         return false;
     }
     $varTagValues = $this->getPropertyTagValues($className, $propertyName, 'var');
     if (count($varTagValues) > 1) {
         throw new InvalidPropertyTypeException('More than one @var annotation given for "' . $className . '::$' . $propertyName . '"', 1367334366);
     }
     $declaredType = strtok(trim(current($varTagValues), " \n\t"), " \n\t");
     try {
         TypeHandling::parseType($declaredType);
     } catch (InvalidTypeException $exception) {
         throw new \InvalidArgumentException(sprintf($exception->getMessage(), 'class "' . $className . '" for property "' . $propertyName . '"'), 1315564475);
     }
     if ($this->isPropertyAnnotatedWith($className, $propertyName, ORM\Id::class)) {
         $skipArtificialIdentity = true;
     }
     $classSchema->addProperty($propertyName, $declaredType, $this->isPropertyAnnotatedWith($className, $propertyName, Flow\Lazy::class), $this->isPropertyAnnotatedWith($className, $propertyName, Flow\Transient::class));
     if ($this->isPropertyAnnotatedWith($className, $propertyName, Flow\Identity::class)) {
         $classSchema->markAsIdentityProperty($propertyName);
     }
     return $skipArtificialIdentity;
 }