i am trying to use retrievalqa from langchain to implement a chatmodel.while using the retrievalQA i get know that there is no option to add the retrival. how to add the retrieval in retrivalqa
vectordb=Weaviate(client,'Document', 'page_content') qa_chain = RetrievalQA.from_chain_type(OpenAI(temperature=0),chain_type_kwargs={"prompt":PROMPT},chain_type="stuff", ) no option to add retriever
