Get the Parent Id of the document

        :param resource: resource name
        :param document: document containing the parent id

def get_parent_id(self, resource, document):
        """Get the Parent Id of the document

        :param resource: resource name
        :param document: document containing the parent id
        """
        parent_type = self._get_parent_type(resource)
        if parent_type and document:
            return document.get(parent_type.get('field'))

        return None