langchain/vectorstores/tair.py/Tair/from_existing_index
class Tair:    def from_existing_index(
        cls,
        embedding: Embeddings,
        index_name: str = "langchain",
        content_key: str = "content",
        metadata_key: str = "metadata",
        **kwargs: Any,
    ) -> Tair:
        """Connect to an existing Tair index."""
        url = get_from_dict_or_env(kwargs, "tair_url", "TAIR_URL")

        search_params = {}
        if "search_params" in kwargs:
            search_params = kwargs.pop("search_params")

        return cls(
            embedding,
            url,
            index_name,
            content_key=content_key,
            metadata_key=metadata_key,
            search_params=search_params,
            **kwargs,
        )