langchain/templates/rag-lantern/README.md

rag_lantern

This template performs RAG with Lantern.

Lantern is an open-source vector database built on top of PostgreSQL. It enables vector search and embedding generation inside your database.

Environment Setup

Set the OPENAI_API_KEY environment variable to access the OpenAI models.

To get your OPENAI_API_KEY, navigate to API keys on your OpenAI account and create a new secret key.

To find your LANTERN_URL and LANTERN_SERVICE_KEY, head to your Lantern project's API settings.

• LANTERN_URL corresponds to the Project URL
• LANTERN_SERVICE_KEY corresponds to the service_role API key

export LANTERN_URL=
export LANTERN_SERVICE_KEY=
export OPENAI_API_KEY=

Setup Lantern Database

Use these steps to setup your Lantern database if you haven't already.

1. Head to https://lantern.dev to create your Lantern database.

2. In your favorite SQL client, jump to the SQL editor and run the following script to setup your database as a vector store:

   -- Create a table to store your documents
   create table
     documents (
       id uuid primary key,
       content text, -- corresponds to Document.pageContent
       metadata jsonb, -- corresponds to Document.metadata
       embedding REAL[1536] -- 1536 works for OpenAI embeddings, change as needed
     );
   
   -- Create a function to search for documents
   create function match_documents (
     query_embedding REAL[1536],
     filter jsonb default '{}'
   ) returns table (
     id uuid,
     content text,
     metadata jsonb,
     similarity float
   ) language plpgsql as $$
   #variable_conflict use_column
   begin
     return query
     select
       id,
       content,
       metadata,
       1 - (documents.embedding <=> query_embedding) as similarity
     from documents
     where metadata @> filter
     order by documents.embedding <=> query_embedding;
   end;
   $$;
   

Setup Environment Variables

Since we are using Lantern and OpenAIEmbeddings, we need to load their API keys.

Usage

First, install the LangChain CLI:

pip install -U langchain-cli

To create a new LangChain project and install this as the only package, you can do:

langchain app new my-app --package rag-lantern

If you want to add this to an existing project, you can just run:

langchain app add rag-lantern

And add the following code to your server.py file:

from rag_lantern.chain import chain as rag_lantern_chain

add_routes(app, rag_lantern_chain, path="/rag-lantern")

(Optional) Let's now configure LangSmith. LangSmith will help us trace, monitor and debug LangChain applications. LangSmith is currently in private beta, you can sign up here. If you don't have access, you can skip this section

export LANGCHAIN_TRACING_V2=true
export LANGCHAIN_API_KEY=<your-api-key>
export LANGCHAIN_PROJECT=<your-project>  # if not specified, defaults to "default"

If you are inside this directory, then you can spin up a LangServe instance directly by:

langchain serve

This will start the FastAPI app with a server is running locally at http://localhost:8000

We can see all templates at http://127.0.0.1:8000/docs We can access the playground at http://127.0.0.1:8000/rag-lantern/playground

We can access the template from code with:

from langserve.client import RemoteRunnable

runnable = RemoteRunnable("http://localhost:8000/rag-lantern")