public function loadClassMetadata(LoadClassMetadataEventArgs $event)
    {
        $metadata = $event->getClassMetadata();
        $reflection = $metadata->getReflectionClass();

        if (null !== $reflection && $reflection->implementsInterface('Sulu\Component\Persistence\Model\UserBlameInterface')) {
            if (!$metadata->hasAssociation(self::CREATOR_FIELD)) {
                $metadata->mapManyToOne([
                    'fieldName' => self::CREATOR_FIELD,
                    'targetEntity' => $this->userClass,
                    'joinColumns' => [
                        [
                            'name' => 'idUsersCreator',
                            'onDelete' => 'SET NULL',
                            'referencedColumnName' => 'id',
                            'nullable' => true,
                        ],
                    ],
                ]);
            }

            if (!$metadata->hasAssociation(self::CHANGER_FIELD)) {
                $metadata->mapManyToOne([
                    'fieldName' => self::CHANGER_FIELD,
                    'targetEntity' => $this->userClass,
                    'joinColumns' => [
                        [
                            'name' => 'idUsersChanger',
                            'onDelete' => 'SET NULL',
                            'referencedColumnName' => 'id',
                            'nullable' => true,
                        ],
                    ],
                ]);
            }
        }
    }