Source code for langchain.retrievers.multi_query

import asyncio
import logging
from typing import List, Optional, Sequence

from langchain_core.callbacks import (
    AsyncCallbackManagerForRetrieverRun,
    CallbackManagerForRetrieverRun,
)
from langchain_core.documents import Document
from langchain_core.language_models import BaseLanguageModel
from langchain_core.output_parsers import BaseOutputParser
from langchain_core.prompts import BasePromptTemplate
from langchain_core.prompts.prompt import PromptTemplate
from langchain_core.retrievers import BaseRetriever
from langchain_core.runnables import Runnable

from langchain.chains.llm import LLMChain

logger = logging.getLogger(__name__)



[docs]
class LineListOutputParser(BaseOutputParser[List[str]]):
    """Output parser for a list of lines."""


[docs]
    def parse(self, text: str) -> List[str]:
        lines = text.strip().split("\n")
        return list(filter(None, lines))  # Remove empty lines




# Default prompt
DEFAULT_QUERY_PROMPT = PromptTemplate(
    input_variables=["question"],
    template="""You are an AI language model assistant. Your task is 
    to generate 3 different versions of the given user 
    question to retrieve relevant documents from a vector  database. 
    By generating multiple perspectives on the user question, 
    your goal is to help the user overcome some of the limitations 
    of distance-based similarity search. Provide these alternative 
    questions separated by newlines. Original question: {question}""",
)


def _unique_documents(documents: Sequence[Document]) -> List[Document]:
    return [doc for i, doc in enumerate(documents) if doc not in documents[:i]]



[docs]
class MultiQueryRetriever(BaseRetriever):
    """Given a query, use an LLM to write a set of queries.

    Retrieve docs for each query. Return the unique union of all retrieved docs.
    """

    retriever: BaseRetriever
    llm_chain: Runnable
    verbose: bool = True
    parser_key: str = "lines"
    """DEPRECATED. parser_key is no longer used and should not be specified."""
    include_original: bool = False
    """Whether to include the original query in the list of generated queries."""


[docs]
    @classmethod
    def from_llm(
        cls,
        retriever: BaseRetriever,
        llm: BaseLanguageModel,
        prompt: BasePromptTemplate = DEFAULT_QUERY_PROMPT,
        parser_key: Optional[str] = None,
        include_original: bool = False,
    ) -> "MultiQueryRetriever":
        """Initialize from llm using default template.

        Args:
            retriever: retriever to query documents from
            llm: llm for query generation using DEFAULT_QUERY_PROMPT
            prompt: The prompt which aims to generate several different versions
                of the given user query
            include_original: Whether to include the original query in the list of
                generated queries.

        Returns:
            MultiQueryRetriever
        """
        output_parser = LineListOutputParser()
        llm_chain = prompt | llm | output_parser
        return cls(
            retriever=retriever,
            llm_chain=llm_chain,
            include_original=include_original,
        )


    async def _aget_relevant_documents(
        self,
        query: str,
        *,
        run_manager: AsyncCallbackManagerForRetrieverRun,
    ) -> List[Document]:
        """Get relevant documents given a user query.

        Args:
            query: user query

        Returns:
            Unique union of relevant documents from all generated queries
        """
        queries = await self.agenerate_queries(query, run_manager)
        if self.include_original:
            queries.append(query)
        documents = await self.aretrieve_documents(queries, run_manager)
        return self.unique_union(documents)


[docs]
    async def agenerate_queries(
        self, question: str, run_manager: AsyncCallbackManagerForRetrieverRun
    ) -> List[str]:
        """Generate queries based upon user input.

        Args:
            question: user query

        Returns:
            List of LLM generated queries that are similar to the user input
        """
        response = await self.llm_chain.ainvoke(
            {"question": question}, config={"callbacks": run_manager.get_child()}
        )
        if isinstance(self.llm_chain, LLMChain):
            lines = response["text"]
        else:
            lines = response
        if self.verbose:
            logger.info(f"Generated queries: {lines}")
        return lines



[docs]
    async def aretrieve_documents(
        self, queries: List[str], run_manager: AsyncCallbackManagerForRetrieverRun
    ) -> List[Document]:
        """Run all LLM generated queries.

        Args:
            queries: query list

        Returns:
            List of retrieved Documents
        """
        document_lists = await asyncio.gather(
            *(
                self.retriever.ainvoke(
                    query, config={"callbacks": run_manager.get_child()}
                )
                for query in queries
            )
        )
        return [doc for docs in document_lists for doc in docs]


    def _get_relevant_documents(
        self,
        query: str,
        *,
        run_manager: CallbackManagerForRetrieverRun,
    ) -> List[Document]:
        """Get relevant documents given a user query.

        Args:
            query: user query

        Returns:
            Unique union of relevant documents from all generated queries
        """
        queries = self.generate_queries(query, run_manager)
        if self.include_original:
            queries.append(query)
        documents = self.retrieve_documents(queries, run_manager)
        return self.unique_union(documents)


[docs]
    def generate_queries(
        self, question: str, run_manager: CallbackManagerForRetrieverRun
    ) -> List[str]:
        """Generate queries based upon user input.

        Args:
            question: user query

        Returns:
            List of LLM generated queries that are similar to the user input
        """
        response = self.llm_chain.invoke(
            {"question": question}, config={"callbacks": run_manager.get_child()}
        )
        if isinstance(self.llm_chain, LLMChain):
            lines = response["text"]
        else:
            lines = response
        if self.verbose:
            logger.info(f"Generated queries: {lines}")
        return lines



[docs]
    def retrieve_documents(
        self, queries: List[str], run_manager: CallbackManagerForRetrieverRun
    ) -> List[Document]:
        """Run all LLM generated queries.

        Args:
            queries: query list

        Returns:
            List of retrieved Documents
        """
        documents = []
        for query in queries:
            docs = self.retriever.invoke(
                query, config={"callbacks": run_manager.get_child()}
            )
            documents.extend(docs)
        return documents



[docs]
    def unique_union(self, documents: List[Document]) -> List[Document]:
        """Get unique Documents.

        Args:
            documents: List of retrieved Documents

        Returns:
            List of unique retrieved Documents
        """
        return _unique_documents(documents)