Check wether the database contains a document matching a condition or
        an ID.

        If ``eids`` is set, it checks if the db contains a document with one
        of the specified.

        :param cond: the condition use
        :type cond: Query
        :param doc_ids: the document IDs to look for

def contains(self, cond=None, doc_ids=None, eids=None):
        """
        Check wether the database contains a document matching a condition or
        an ID.

        If ``eids`` is set, it checks if the db contains a document with one
        of the specified.

        :param cond: the condition use
        :type cond: Query
        :param doc_ids: the document IDs to look for
        """
        doc_ids = _get_doc_ids(doc_ids, eids)

        if doc_ids is not None:
            # Documents specified by ID
            return any(self.get(doc_id=doc_id) for doc_id in doc_ids)

        # Document specified by condition
        return self.get(cond) is not None