Hotels LLM Demo with LangChain, AstraPy and Astra DB

What

A full demo app (API + front-end) to search and review hotels, powered by GenAI, LLMs and embedding vectors.

The demo features:

• LLM-processed user profile;
• vector-search-powered hotel review search;
• LLM-generated hotel summaries based on reviews + user profile (to maximize relevance);
• caching of prompt/response LLM interactions.

Tech stack:

• Astra DB as the vector database;
• OpenAI for the LLM and the embeddings;
• React+Typescript for the client;
• FastAPI, RAGStack, LangChain and AstraPy for the API.

Prerequisites

You need:

• an Astra DB Database (free tier is fine!). Find and copy, from the Astra UI, the two required connection credentials: the API Endpoint (e.g. https://....apps.astra.datastax.com) and the Token (AstraCS:...).
• an OpenAI API Key. (More info here, note that out-of-the-box this demo supports OpenAI unless you tinker with the code.)

How-to (Gitpod)

Click this button, confirm opening of the workspace (you might need to do a Gitpod login in the process) and wait 3-4 minutes for the full setup to complete: instructions will show up in the console below, where you'll have to provide connection details and OpenAI key when prompted.

In the meantime, the app will open in the top panel. We recommend opening the app in a new browser tab for a better view, using the link that will be provided in the bottom console once everything is ready.

Once you see the Uvicorn running on [address:port] message, the API is ready and you can start using the client.

How-to (local run)

Setup (API)

Create a python3.8+ virtualenv and pip install -r requirements.txt.

Note: this demo has been tested with Python versions 3.8, 3.9 and 3.10. Please stick to these Python versions, otherwise you'll likely be unable to install all required dependencies (until newer wheels for them are published).

Copy .env.template to .env and fill the values (see Prerequisites above).

Prepare database

There are a few scripts to run in sequence which create the necessary collections on the database and fill them with data. Simply launch the following scripts one after the other (the script names make it clear what part of the setup they do):

python -m setup.2-populate-review-vector-collection
python -m setup.3-populate-hotels-and-cities-collections
python -m setup.4-create-users-collection
python -m setup.5-populate-reviews-collection

Note: the repo comes with a dataset ready for ingestion in the DB, i.e. already cleaned and made into the correct format (including the embedding calculation!). If you are curious about how that was prepared, we have included the scripts for that - which you do not need to run, to be clear.

Show me the dataset preprocessing steps, I'm curious

Download the dataset

Download Datafiniti_Hotel_Reviews_Jun19.csv from here (unzip if necessary) and put it into setup/original.

Clean the input CSV

Refine the original CSV into its "cleaned" version for later use:

python -m setup.0-clean-csv

Calculate embeddings (takes time and some OpenAI calls!)

This script calculates embedding vectors for all reviews (it actually combines review title and body in a certain way, and the resulting string is what is sent to the embedding OpenAI service):

python -m setup.1-augment-with-embeddings

Note: this step is time-consuming and makes use of several calls of your OpenAI account. This is why, to save time and (your) money, the script stores the resulting vectors in a precalculated_embeddings.json file (which uses a custom compression scheme, see the code!), so that the "populate review vector collection" step does not need to calculate them anymore. We included the precalculated embeddings in the repo: this is why you can start the setup from step 2.

Launch the API

In the console with the virtual environment active, run:

uvicorn api:app
# (optionally add "--reload")

Once you see the Uvicorn running on [address:port] message, the API is ready and you can start using the client.

Client

Setup

Note: you need a recent version of Node.js installed.

On another console, go to the client directory and run npm install to get all dependencies.

Start the client

Issue the command

npm start

If it does not open by itself, go to localhost:3000 on your browser.

Note: if you start the API on another address/port, you can specify it like this instead:

REACT_APP_API_BASE_URL="http://10.1.1.2:6789" npm start

Note: do not worry if you see some API requests being done twice. This is due to the React (v18+) app running in dev mode with use strict. See here for more. Behaviour in production would be all right.

Cleanup

Should you remove completely all artifacts created by the app on your database (including any new review you may have added for a hotel), you can run this:

python -m setup.cleanup-delete-all-collections

Development

Make sure you pip install -r requirements-dev.txt as well.

Checks

isort . --profile black
black .
mypy .

TODOs

• Check readme and other writeups + slides. Ensure they reflect latest
• Check gitpod and transition to RAGStack
• Client: migrate to consistent interfaces, remove redundant interfaces.
• Recheck the not-to-be-repeated init setup steps
• Fix: when searching hotels with empty fields, goes back to "login" page
• Replace github prebuilds with the "project settings" (the former is deprecated now)
• Rewrite the summarization by factoring something like this: https://python.langchain.com/docs/use_cases/summarization/#option-1.-stuff (there are three chain.invoke(...) in this code now)