langchain/templates/rag-lancedb/rag_lancedb/chain.py

from langchain_community.vectorstores import LanceDB
from langchain_core.output_parsers import StrOutputParser
from langchain_core.prompts import ChatPromptTemplate
from langchain_core.pydantic_v1 import BaseModel
from langchain_core.runnables import RunnableParallel, RunnablePassthrough
from langchain_openai import ChatOpenAI, OpenAIEmbeddings

# Example for document loading (from url), splitting, and creating vectostore

""" 
# Load
from langchain_community.document_loaders import WebBaseLoader
loader = WebBaseLoader("https://lilianweng.github.io/posts/2023-06-23-agent/")
data = loader.load()

# Split
from langchain.text_splitter import RecursiveCharacterTextSplitter
text_splitter = RecursiveCharacterTextSplitter(chunk_size=500, chunk_overlap=0)
all_splits = text_splitter.split_documents(data)

# Add to vectorDB
vectorstore = LanceDB.from_documents(documents=all_splits,
                             embedding=OpenAIEmbeddings())
retriever = vectorstore.as_retriever()
"""

# Embed a single document for test
vectorstore = LanceDB.from_texts(
    ["harrison worked at kensho"], embedding=OpenAIEmbeddings()
)

retriever = vectorstore.as_retriever()

# RAG prompt
template = """Answer the question based only on the following context:
{context}

Question: {question}
"""
prompt = ChatPromptTemplate.from_template(template)

# LLM
model = ChatOpenAI()

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


class Question(BaseModel):
    __root__: str


chain = chain.with_types(input_type=Question)