private function getRelationships(FullyQualifiedClassName $fullyQualifiedClassName): array
    {
        $fields = (string)$fullyQualifiedClassName;
        if (!is_subclass_of($fields, CommonSectionInterface::class)) {
            throw new NotASexyFieldEntityException;
        }
        /** @var CommonSectionInterface $fields */
        $relationships = [];
        foreach ($fields::fieldInfo() as $field) {
            if (!is_null($field['relationship'])) {
                $relationships[] = $field['relationship']['class'];
            }
        }
        return $relationships;
    }