How can I integrate a system message into ChatOpenAI using LangChain prompt templates?

You can include a system-level instruction by incorporating it into your chat prompt rather than passing it directly to ChatOpenAI. LangChain provides prompt templates that let you define a sequence of messages—including system messages. For example, you can use ChatPromptTemplate to insert your system message:

PYTHONCopied
from langchain_core.prompts import ChatPromptTemplate
from langchain_openai import ChatOpenAI
from langchain_chains import RetrievalQA

# Define your system and user messages in a structured prompt
prompt = ChatPromptTemplate.from_messages(
    [
        ("system", "you are the author of the book"),
        ("user", "{input}")
    ]
)

# Initialize your ChatOpenAI LLM
llm = ChatOpenAI(model_name="gpt-3.5-turbo", temperature=0.5)

# Configure your retriever from Pinecone
retriever = vector_store.as_retriever(search_type="similarity", search_kwarks={"K": 4})

# Create a RetrievalQA chain that uses the custom prompt template
chain = RetrievalQA.from_chain_type(llm=llm, chain_type="stuff", retriever=retriever, prompt=prompt)

# Run your chain with the user query
answer = chain.run(q)
return answer

In this example, the system message ("you are the author of the book") is part of the prompt template. When combined with the user’s input, the language model will follow the behavior defined by the system message throughout the conversation. This approach works well to instruct the model in scenarios like impersonating the book's author.