🐍 Proxy Pattern Demo: Client and Orders (PostgreSQL/SQLAlchemy)

This project demonstrates the implementation of the Virtual Proxy Pattern (Lazy Initialization) in Python, using SQLAlchemy to simulate database access (PostgreSQL).
The main goal is to control the loading of a high-cost domain object (ClientORM) only at the moment it is truly needed, improving performance.

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📁 Project Structure

The source code is isolated within the app/ package structure, following standard Python packaging practices.

/proxy-project
├── .env                  # PostgreSQL connection environment variables
├── requirements.txt      # Project dependencies
└── app/                  # Main Python Package
    ├── client.py         # Application Entry Point (GUI and Console Demo)
    ├── init_db.py        # Creates the Clients and Orders tables
    ├── cleanup_db.py     # **NEW:** Removes all tables (required for full reset)
    ├── seed_db.py        # **NEW:** Populates the DB with 1000 test clients
    └── src/
        ├── core/         # Domain Logic (Proxy, ORM Models)
        │   ├── client_proxy.py # The Virtual Proxy implementation
        │   ├── clientORM.py  # The Real Subject (SQLAlchemy Model)
        │   ├── model.py    # Database Configuration (Engine, Session)
        │   └── order.py    # Order Data Model
        └── gui/          # Presentation Layer (Tkinter App)
            └── client_gui.py

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🛠️ Setup and Installation

1. Requirements

Ensure you have Python 3.8+ installed and a PostgreSQL server running locally (default port 5432).

2. Environment Variables

Create or update the .env file inside the app/ directory (/proxy-project/app/.env) with your database credentials:

# .env content example
DB_HOST=localhost
DB_PORT=5432
DB_NAME=futino
DB_USER=postgres
DB_PASSWORD=supra
DB_DRIVER=psycopg2

3. Python Dependencies

Install the necessary libraries using requirements.txt:

pip install -r requirements.txt

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🚀 How to Run

All scripts must be executed from the project root directory (/proxy-project/) using Python's module notation (python -m).

1. Initialize and Seed the Database

Before running the application, you must create the tables and insert the test data (1000 clients and 2000 orders).

Command	Description
python -m app.init_db	Creates the clients and orders tables in the database.
python -m app.seed_db	Inserts 1000 clients and 2000 orders (test data). (Requires empty tables!)

Data Cleanup (Required after "UniqueViolation" errors)
If you need to re-run seed_db after a duplicate key error, clear the tables using:

python -m app.cleanup_db
python -m app.init_db
python -m app.seed_db

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2. Start the Demo Application

Execute the main entry point, which loads the graphical interface (ClientApp / Tkinter):

python -m app.client

When interacting with the GUI, observe the log (bottom part of the window) to see when the Proxy is:

• Lazy Initializing: Loading the ClientORM object from the database (only when you click "Access Name").
• Lazy Loading: Fetching the list of orders via SQLAlchemy (only when you click "Access Orders").