langchain/retrievers/vespa_retriever.py/VespaRetriever/get_relevant_documents_with_filter
class VespaRetriever:    def get_relevant_documents_with_filter(
        self, query: str, *, _filter: Optional[str] = None
    ) -> List[Document]:
        body = self._query_body.copy()
        _filter = f" and {_filter}" if _filter else ""
        body["yql"] = body["yql"] + _filter
        body["query"] = query
        return self._query(body)