langchain/templates/neo4j-cypher-memory/neo4j_cypher_memory/chain.py

from typing import Any, Dict, List

from langchain.chains.graph_qa.cypher_utils import CypherQueryCorrector, Schema
from langchain.memory import ChatMessageHistory
from langchain_community.chat_models import ChatOpenAI
from langchain_community.graphs import Neo4jGraph
from langchain_core.output_parsers import StrOutputParser
from langchain_core.prompts import ChatPromptTemplate, MessagesPlaceholder
from langchain_core.pydantic_v1 import BaseModel
from langchain_core.runnables import RunnablePassthrough

# Connection to Neo4j
graph = Neo4jGraph()

# Cypher validation tool for relationship directions
corrector_schema = [
    Schema(el["start"], el["type"], el["end"])
    for el in graph.structured_schema.get("relationships")
]
cypher_validation = CypherQueryCorrector(corrector_schema)

# LLMs
cypher_llm = ChatOpenAI(model="gpt-4", temperature=0.0)
qa_llm = ChatOpenAI(model="gpt-3.5-turbo", temperature=0.0)


def convert_messages(input: List[Dict[str, Any]]) -> ChatMessageHistory:
    history = ChatMessageHistory()
    for item in input:
        history.add_user_message(item["result"]["question"])
        history.add_ai_message(item["result"]["answer"])
    return history


def get_history(input: Dict[str, Any]) -> ChatMessageHistory:
    input.pop("question")
    # Lookback conversation window
    window = 3
    data = graph.query(
        """
    MATCH (u:User {id:$user_id})-[:HAS_SESSION]->(s:Session {id:$session_id}),
                       (s)-[:LAST_MESSAGE]->(last_message)
    MATCH p=(last_message)<-[:NEXT*0.."""
        + str(window)
        + """]-()
    WITH p, length(p) AS length
    ORDER BY length DESC LIMIT 1
    UNWIND reverse(nodes(p)) AS node
    MATCH (node)-[:HAS_ANSWER]->(answer)
    RETURN {question:node.text, answer:answer.text} AS result
 """,
        params=input,
    )
    history = convert_messages(data)
    return history.messages


def save_history(input):
    input.pop("response")
    # store history to database
    graph.query(
        """MERGE (u:User {id: $user_id})
WITH u                
OPTIONAL MATCH (u)-[:HAS_SESSION]->(s:Session{id: $session_id}),
                (s)-[l:LAST_MESSAGE]->(last_message)
FOREACH (_ IN CASE WHEN last_message IS NULL THEN [1] ELSE [] END |
CREATE (u)-[:HAS_SESSION]->(s1:Session {id:$session_id}),
    (s1)-[:LAST_MESSAGE]->(q:Question {text:$question, cypher:$query, date:datetime()}),
        (q)-[:HAS_ANSWER]->(:Answer {text:$output}))                                
FOREACH (_ IN CASE WHEN last_message IS NOT NULL THEN [1] ELSE [] END |
CREATE (last_message)-[:NEXT]->(q:Question 
                {text:$question, cypher:$query, date:datetime()}),
                (q)-[:HAS_ANSWER]->(:Answer {text:$output}),
                (s)-[:LAST_MESSAGE]->(q)
DELETE l)                """,
        params=input,
    )

    # Return LLM response to the chain
    return input["output"]


# Generate Cypher statement based on natural language input
cypher_template = """This is important for my career.
Based on the Neo4j graph schema below, write a Cypher query that would answer the user's question:
{schema}

Question: {question}
Cypher query:"""  # noqa: E501

cypher_prompt = ChatPromptTemplate.from_messages(
    [
        (
            "system",
            "Given an input question, convert it to a Cypher query. No pre-amble.",
        ),
        MessagesPlaceholder(variable_name="history"),
        ("human", cypher_template),
    ]
)

cypher_response = (
    RunnablePassthrough.assign(schema=lambda _: graph.get_schema, history=get_history)
    | cypher_prompt
    | cypher_llm.bind(stop=["\nCypherResult:"])
    | StrOutputParser()
)

# Generate natural language response based on database results
response_template = """Based on the the question, Cypher query, and Cypher response, write a natural language response:
Question: {question}
Cypher query: {query}
Cypher Response: {response}"""  # noqa: E501

response_prompt = ChatPromptTemplate.from_messages(
    [
        (
            "system",
            "Given an input question and Cypher response, convert it to a "
            "natural language answer. No pre-amble.",
        ),
        ("human", response_template),
    ]
)

chain = (
    RunnablePassthrough.assign(query=cypher_response)
    | RunnablePassthrough.assign(
        response=lambda x: graph.query(cypher_validation(x["query"])),
    )
    | RunnablePassthrough.assign(
        output=response_prompt | qa_llm | StrOutputParser(),
    )
    | save_history
)

# Add typing for input


class Question(BaseModel):
    question: str
    user_id: str
    session_id: str


chain = chain.with_types(input_type=Question)