Amazon Neptune is a high-performance graph analytics and serverless database for superior scalability and availability. This example shows the QA chain that queries the Neptune graph database using openCypher and returns a human-readable response. Cypher is a declarative graph query language that allows for expressive and efficient data querying in a property graph. openCypher is an open-source implementation of Cypher.# Neptune Open Cypher QA Chain This QA chain queries Amazon Neptune using openCypher and returns human readable response
LangChain supports both Neptune Database and Neptune Analytics with create_neptune_opencypher_qa_chain. Neptune Database is a serverless graph database designed for optimal scalability and availability. It provides a solution for graph database workloads that need to scale to 100,000 queries per second, Multi-AZ high availability, and multi-Region deployments. You can use Neptune Database for social networking, fraud alerting, and Customer 360 applications. Neptune Analytics is an analytics database engine that can quickly analyze large amounts of graph data in memory to get insights and find trends. Neptune Analytics is a solution for quickly analyzing existing graph databases or graph datasets stored in a data lake. It uses popular graph analytic algorithms and low-latency analytic queries.

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Using Neptune Database

from langchain_aws.graphs import NeptuneGraph

host = "<neptune-host>"
port = 8182
use_https = True

graph = NeptuneGraph(host=host, port=port, use_https=use_https)

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Using Neptune Analytics

from langchain_aws.graphs import NeptuneAnalyticsGraph

graph = NeptuneAnalyticsGraph(graph_identifier="<neptune-analytics-graph-id>")

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Using the Neptune openCypher QA Chain

This QA chain queries the Neptune graph database using openCypher and returns a human-readable response. 
from langchain_aws import ChatBedrockConverse
from langchain_aws.chains import create_neptune_opencypher_qa_chain

MODEL_ID = "anthropic.claude-3-5-sonnet-20241022-v2:0"
llm = ChatBedrockConverse(
    model=MODEL_ID,
    temperature=0,
)

chain = create_neptune_opencypher_qa_chain(llm=llm, graph=graph)

result = chain.invoke("How many outgoing routes does the Austin airport have?")
print(result["result"].content)

Austin airport has 98 outgoing routes.

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Adding Message History

The Neptune openCypher QA chain has the ability to be wrapped by RunnableWithMessageHistory. This adds message history to the chain, allowing us to create a chatbot that retains conversation state across multiple invocations. To start, we need a way to store and load the message history. For this purpose, each thread will be created as an instance of InMemoryChatMessageHistory, and stored into a dictionary for repeated access. (Also see: https://python.langchain.com/docs/versions/migrating_memory/chat_history/#chatmessagehistory) 
from langchain_core.chat_history import InMemoryChatMessageHistory

chats_by_session_id = {}


def get_chat_history(session_id: str) -> InMemoryChatMessageHistory:
    chat_history = chats_by_session_id.get(session_id)
    if chat_history is None:
        chat_history = InMemoryChatMessageHistory()
        chats_by_session_id[session_id] = chat_history
    return chat_history
Now, the QA chain and message history storage can be used to create the new RunnableWithMessageHistory. Note that we must set query as the input key to match the format expected by the base chain. 
from langchain_core.runnables.history import RunnableWithMessageHistory

runnable_with_history = RunnableWithMessageHistory(
    chain,
    get_chat_history,
    input_messages_key="query",
)
Before invoking the chain, a unique session_id needs to be generated for the conversation that the new InMemoryChatMessageHistory will remember. 
import uuid

session_id = uuid.uuid4()
Finally, invoke the message history enabled chain with the session_id. 
result = runnable_with_history.invoke(
    {"query": "How many destinations can I fly to directly from Austin airport?"},
    config={"configurable": {"session_id": session_id}},
)
print(result["result"].content)

You can fly directly to 98 destinations from Austin airport.
As the chain continues to be invoked with the same session_id, responses will be returned in the context of previous queries in the conversation. 
result = runnable_with_history.invoke(
    {"query": "Out of those destinations, how many are in Europe?"},
    config={"configurable": {"session_id": session_id}},
)
print(result["result"].content)

You can fly directly to 4 destinations in Europe from Austin airport.

result = runnable_with_history.invoke(
    {"query": "Give me the codes and names of those airports."},
    config={"configurable": {"session_id": session_id}},
)
print(result["result"].content)

The four European destinations you can fly to directly from Austin airport are:
- AMS (Amsterdam Airport Schiphol)
- FRA (Frankfurt am Main)
- LGW (London Gatwick)
- LHR (London Heathrow)