RetrievalQA

Chain for question-answering against an index.

This class is deprecated. See below for an example implementation using create_retrieval_chain:

from langchain_classic.chains import create_retrieval_chain
from langchain_classic.chains.combine_documents import (
    create_stuff_documents_chain,
)
from langchain_core.prompts import ChatPromptTemplate
from langchain_openai import ChatOpenAI

retriever = ...  # Your retriever
model = ChatOpenAI()

system_prompt = (
    "Use the given context to answer the question. "
    "If you don't know the answer, say you don't know. "
    "Use three sentence maximum and keep the answer concise. "
    "Context: {context}"
)
prompt = ChatPromptTemplate.from_messages(
    [
        ("system", system_prompt),
        ("human", "{input}"),
    ]
)
question_answer_chain = create_stuff_documents_chain(model, prompt)
chain = create_retrieval_chain(retriever, question_answer_chain)

chain.invoke({"input": query})