langchain/templates/rag-vectara-multiquery/rag_vectara_multiquery/chain.py

import os

from langchain.chat_models import ChatOpenAI
from langchain.prompts import ChatPromptTemplate
from langchain.retrievers.multi_query import MultiQueryRetriever
from langchain.vectorstores import Vectara
from langchain_core.output_parsers import StrOutputParser
from langchain_core.pydantic_v1 import BaseModel
from langchain_core.runnables import RunnableParallel, RunnablePassthrough

if os.environ.get("VECTARA_CUSTOMER_ID", None) is None:
    raise Exception("Missing `VECTARA_CUSTOMER_ID` environment variable.")
if os.environ.get("VECTARA_CORPUS_ID", None) is None:
    raise Exception("Missing `VECTARA_CORPUS_ID` environment variable.")
if os.environ.get("VECTARA_API_KEY", None) is None:
    raise Exception("Missing `VECTARA_API_KEY` environment variable.")

# If you want to ingest data then use this code.
# Note that no document chunking is needed, as this is
# done efficiently in the Vectara backend.
# Note: you will need to install beautifulsoup4 to ingest

# from langchain.document_loaders import WebBaseLoader
# from langchain.embeddings import OpenAIEmbeddings
# loader = WebBaseLoader("https://lilianweng.github.io/posts/2023-06-23-agent/")
# docs = loader.load()
# vec_store = Vectara.from_documents(docs, embedding=OpenAIEmbeddings())
# retriever = vec_store.as_retriever()

# Otherwise, if data is already loaded into Vectara then use this code:
llm = ChatOpenAI(temperature=0)
retriever = MultiQueryRetriever.from_llm(retriever=Vectara().as_retriever(), llm=llm)

# RAG prompt
template = """Answer the question based only on the following context:
{context}
Question: {question}
"""
prompt = ChatPromptTemplate.from_template(template)

# RAG
model = ChatOpenAI()
chain = (
    RunnableParallel({"context": retriever, "question": RunnablePassthrough()})
    | prompt
    | model
    | StrOutputParser()
)


# Add typing for input
class Question(BaseModel):
    __root__: str


chain = chain.with_types(input_type=Question)