ApiPlatform\Core\Bridge\Symfony\Routing\IriConverter::getIdentifiersFromItem PHP Method

    private function getIdentifiersFromItem($item) : array
    {
        $identifiers = [];
        $resourceClass = $this->getObjectClass($item);
        foreach ($this->propertyNameCollectionFactory->create($resourceClass) as $propertyName) {
            $propertyMetadata = $this->propertyMetadataFactory->create($resourceClass, $propertyName);
            $identifier = $propertyMetadata->isIdentifier();
            if (null === $identifier || false === $identifier) {
                continue;
            }
            $identifiers[$propertyName] = $this->propertyAccessor->getValue($item, $propertyName);
            if (!is_object($identifiers[$propertyName])) {
                continue;
            }
            $relatedResourceClass = $this->getObjectClass($identifiers[$propertyName]);
            $relatedItem = $identifiers[$propertyName];
            unset($identifiers[$propertyName]);
            foreach ($this->propertyNameCollectionFactory->create($relatedResourceClass) as $relatedPropertyName) {
                $propertyMetadata = $this->propertyMetadataFactory->create($relatedResourceClass, $relatedPropertyName);
                if ($propertyMetadata->isIdentifier()) {
                    if (isset($identifiers[$propertyName])) {
                        throw new RuntimeException(sprintf('Composite identifiers not supported in "%s" through relation "%s" of "%s" used as identifier', $relatedResourceClass, $propertyName, $resourceClass));
                    }
                    $identifiers[$propertyName] = $this->propertyAccessor->getValue($relatedItem, $relatedPropertyName);
                }
            }
            if (!isset($identifiers[$propertyName])) {
                throw new RuntimeException(sprintf('No identifier found in "%s" through relation "%s" of "%s" used as identifier', $relatedResourceClass, $propertyName, $resourceClass));
            }
        }
        return $identifiers;
    }