Build an LLM RAG Chatbot With LangChain :

Build an LLM RAG Chatbot With LangChain
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You’ve likely interacted with large language models (LLMs), like the ones behind OpenAI’s ChatGPT, and experienced their remarkable ability to answer questions, summarize documents, write code, and much more. While LLMs are remarkable by themselves, with a little programming knowledge, you can leverage libraries like LangChain to create your own LLM-powered chatbots that can do just about anything.

In an enterprise setting, one of the most popular ways to create an LLM-powered chatbot is through retrieval-augmented generation (RAG). When you design a RAG system, you use a retrieval model to retrieve relevant information, usually from a database or corpus, and provide this retrieved information to an LLM to generate contextually relevant responses.

In this tutorial, you’ll step into the shoes of an AI engineer working for a large hospital system. You’ll build a RAG chatbot in LangChain that uses Neo4j to retrieve data about the patients, patient experiences, hospital locations, visits, insurance payers, and physicians in your hospital system.

In this tutorial, you’ll learn how to:

  • Use LangChain to build custom chatbots
  • Design a chatbot using your understanding of the business requirements and hospital system data
  • Work with graph databases
  • Set up a Neo4j AuraDB instance
  • Build a RAG chatbot that retrieves both structured and unstructured data from Neo4j
  • Deploy your chatbot with FastAPI and Streamlit

Click the link below to download the complete source code and data for this project:

Demo: An LLM RAG Chatbot With LangChain and Neo4j

By the end of this tutorial, you’ll have a REST API that serves your LangChain chatbot. You’ll also have a Streamlit app that provides a nice chat interface to interact with your API:

Under the hood, the Streamlit app sends your messages to the chatbot API, and the chatbot generates and sends a response back to the Streamlit app, which displays it to the user.

You’ll get an in-depth overview of the data that your chatbot has access to later, but if you’re anxious to test it out, you can ask questions similar to the examples given in the sidebar:

Example questions that the chatbot can answer
Example questions can be found in the sidebar.

You’ll learn how to tackle each step, from understanding the business requirements and data to building the Streamlit app. There’s a lot to unpack in this tutorial, but don’t feel overwhelmed. You’ll get some background on each concept introduced, along with links to external sources that will deepen your understanding. Now, it’s time to dive in!


This tutorial is best suited for intermediate Python developers who want to get hands-on experience creating custom chatbots. Aside from intermediate Python knowledge, you’ll benefit from having a high-level understanding of the following concepts and technologies:

Nothing listed above is a hard prerequisite, so don’t worry if you don’t feel knowledgeable in any of them. You’ll be introduced to each concept and technology along the way. Besides, there’s no better way to learn these prerequisites than to implement them yourself in this tutorial.

Next up, you’ll get a brief project overview and begin learning about LangChain.

Project Overview

Throughout this tutorial, you’ll create a few directories that make up your final chatbot. Here’s a breakdown of each directory:

  • langchain_intro/ will help you get familiar with LangChain and equip you with the tools that you need to build the chatbot you saw in the demo, and it won’t be included in your final chatbot. You’ll cover this in Step 1.

  • data/ has the raw hospital system data stored as CSV files. You’ll explore this data in Step 2. In Step 3, you’ll move this data into a Neo4j database that your chatbot will query to answer questions.

  • hospital_neo4j_etl/ contains a script that loads the raw data from data/ into your Neo4j database. You have to run this before building your chatbot, and you’ll learn everything you need to know about setting up a Neo4j instance in Step 3.

  • chatbot_api/ is your FastAPI app that serves your chatbot as a REST endpoint, and it’s the core deliverable of this project. The chatbot_api/src/agents/ and chatbot_api/src/chains/ subdirectories contain the LangChain objects that comprise your chatbot. You’ll learn what agents and chains are later, but for now, just know that your chatbot is actually a LangChain agent composed of chains and functions.

  • tests/ includes two scripts that test how fast your chatbot can answer a series of questions. This will give you a feel for how much time you save by making asynchronous requests to LLM providers like OpenAI.

  • chatbot_frontend/ is your Streamlit app that interacts with the chatbot endpoint in chatbot_api/. This is the UI that you saw in the demo, and you’ll build this in Step 5.

All the environment variables needed to build and run your chatbot will be stored in a .env file. You’ll deploy the code in hospital_neo4j_etl/, chatbot_api, and chatbot_frontend as Docker containers that’ll be orchestrated with Docker Compose. If you want to experiment with the chatbot before going through the rest of this tutorial, then you can download the materials and follow the instructions in the README file to get things running:

With the project overview and prerequisites behind you, you’re ready to get started with the first step—getting familiar with LangChain.

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March 06, 2024 at 07:30PM
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