📄 Document GPT - FastAPI Backend

This FastAPI backend serves as the core API for handling document uploads, processing PDF files, embedding document content into a vector database (Qdrant), and allowing users to ask questions based on the uploaded document. The AI model uses OpenAI's embeddings to generate intelligent responses from the document content.

🛠️ Features

• PDF Upload: Upload PDF files to be processed and stored in a vector database (Qdrant) for querying.
• Question & Answer System: Users can ask questions based on the content of the uploaded PDF.
• API Documentation: Automatic API documentation available through Swagger at /docs.

📦 Libraries Used

• FastAPI: For building the web API.
• Qdrant Client: For storing and retrieving document embeddings.
• LangChain: For handling PDF processing and embeddings.
• OpenAI: For generating embeddings and AI model responses.
• PyPDFLoader: For extracting text from PDF files.
• CORS Middleware: For handling Cross-Origin Resource Sharing (CORS) to allow frontend requests from different domains.
• dotenv: For managing environment variables (e.g., API keys).

🗂️ Project Structure

• app.py: Main FastAPI application file containing the API endpoints for PDF upload and question-answer system.
• utils.py: Contains utility functions for processing PDF files, sending embeddings to the vector DB, and retrieving answers from the embeddings.
• Environment Variables: API keys for OpenAI and Qdrant are managed through environment variables using .env file.

🚀 Getting Started

Prerequisites

Before setting up the FastAPI backend, ensure you have the following installed:

• Python 3.7+
• Pip (Python package manager)
• Qdrant (a vector database, can be run locally or via a managed service)
• OpenAI API Key (for generating embeddings and responses)
• Virtual environment (optional but recommended)

🛠️ Installation & Setup

Follow these steps to set up the FastAPI backend on your local machine:

Step 1: Clone the Repository

git clone <your-repo-url>
cd <your-repo-name>

Step 2: Set Up a Virtual Environment

It is recommended to create a virtual environment to manage the dependencies:

python3 -m venv venv
source venv/bin/activate  # On Windows: venv\Scripts\activate

Step 3: Install Dependencies

Install the required dependencies using pip:

pip install -r requirements.txt

If there is no requirements.txt file, manually install these packages:

pip install fastapi qdrant-client langchain pydantic uvicorn python-dotenv openai

Step 4: Set Up Environment Variables

Create a .env file in the root directory and add the necessary API keys for OpenAI and Qdrant:

OPENAI_API_KEY=your-openai-api-key
QDRANT_URL=your-qdrant-url
QDRANT_API_KEY=your-qdrant-api-key

• OPENAI_API_KEY: The API key for accessing OpenAI services.
• QDRANT_URL: The URL to your Qdrant instance.
• QDRANT_API_KEY: The API key for Qdrant (if required).

Step 5: Run the FastAPI Application

Start the FastAPI server locally by running the following command:

uvicorn app:app --reload

This will start the server at http://127.0.0.1:8000/.

Step 6: Test the API on Swagger UI

FastAPI automatically generates API documentation, accessible through Swagger. Open your browser and navigate to: http://127.0.0.1:8000/docs

Here you can test both API endpoints directly:

• /upload-pdf/: Upload a PDF file for processing and storage in Qdrant.
• /ask-question/: Ask a question based on the uploaded PDF's content.

📄 API Endpoints

1. Upload PDF - /upload-pdf/ [POST]

Uploads a PDF file, processes it, creates embeddings, and stores them in Qdrant.

Request:

• Method: POST
• Content Type: multipart/form-data
• Body: PDF file to upload.

Response: Success: { "message": "PDF successfully processed and stored in vector DB" } Error: { "detail": "Failed to process PDF: <error-message>" }

2. Ask Question - /ask-question/ [POST]

Accepts a question and returns an answer based on the content stored in the vector database from the uploaded PDF.

Request:

• Method: POST
• Content Type: application/json
• Body:

  {
  "question": "What is the summary of this document?"
  }
  

Response:

Success: { "answer": "<response-from-the-document>" } Error: { "detail": "Failed to retrieve answer: <error-message>" }

3. Health Check - / [GET]

A simple health check endpoint to verify that the API is up and running.

Response:

• Success: { "status": "Success" }

🧑‍💻 Utils Overview

The utils.py file contains utility functions that handle core logic for processing PDFs, sending embeddings to Qdrant, and retrieving answers from stored documents.

Key Functions in utils.py:

1. process_pdf(pdf_path):

   • Extracts the text from the PDF and splits it into smaller chunks.
   • Input: Path to the PDF file.
   • Returns: A list of text chunks from the PDF.

2. send_to_qdrant(documents, embedding_model):

   • Sends the processed document chunks to Qdrant for storage after creating embeddings.
   • Input: List of document chunks and an embedding model.
   • Returns: True if successful, False if there’s an error.

3. qdrant_client():

   • Initializes and returns a Qdrant client for interacting with the vector database.
   • Returns: A configured Qdrant vector store.

4. qa_ret(qdrant_store, input_query):

   • Handles question-answering by retrieving the relevant content from Qdrant and generating a response using OpenAI's GPT model.
   • Input: The Qdrant vector store and the user’s question.
   • Returns: A generated response based on the document’s context.

🧪 Testing the Application

Test PDF Upload

• Start the FastAPI server (uvicorn app:app --reload).
• Use Swagger at http://127.0.0.1:8000/docs to upload a PDF.
• After the PDF is processed, use the /ask-question/ endpoint to ask a question based on the uploaded content.

⚙️ Deployment Considerations

• Ensure environment variables are properly set in your production environment for API keys.
• Use a scalable deployment method like Docker or deploy to a cloud service like AWS, Google Cloud, or Heroku.
• You can deploy Qdrant as a managed service or host your own instance, depending on your requirements.