📝 Portfolio Tracker (SQLite) — Architecture

A Flask web application built following the official Flask tutorial, demonstrating core Flask design patterns: application factory, blueprints, request context, and session management.

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Technology Stack

Layer	Technology	Purpose
Language	Python 3.13+	Application runtime
Web Framework	Flask 3.1.2	Routes, templates, request handling
Database	SQLite3 (built-in)	Lightweight relational database
Templates	Jinja2	Server-side HTML rendering
Password Hashing	Werkzeug	PBKDF2-based password security
Timezone	pytz	UTC → Asia/Singapore conversion
CLI	Click (Flask dependency)	init-db command
Testing	pytest + coverage	Unit tests and code coverage
Build System	Flit	Modern Python packaging

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Application Structure

app_portfolio_tracker/
├── __init__.py          # Application factory (create_app)
├── auth.py              # Authentication blueprint
├── blog.py              # Blog/content blueprint
├── db.py                # Database utilities
├── logic.py             # Business logic (extensible)
├── schema.sql           # Database schema
├── static/
│   └── style.css
└── templates/
    ├── base.html        # Base template with navigation
    ├── auth/
    │   ├── login.html
    │   └── register.html
    └── blog/
        ├── index.html
        ├── create.html
        └── update.html

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Architecture Breakdown

1. Application Factory Pattern

The entry point is create_app() in __init__.py — the Flask application factory:

def create_app(test_config=None):
    app = Flask(__name__, instance_relative_config=True)
    app.config.from_mapping(
        SECRET_KEY='dev',
        DATABASE=os.path.join(app.instance_path, 'portfolio_tracker.sqlite'),
    )
    # Blueprint registration, database init, URL routing
    return app

Why this pattern?

• Enables multiple app instances (testing vs. production)
• Allows dynamic configuration injection
• Prevents circular imports
• Standard Flask best practice

2. Blueprint Architecture

The application is split into two blueprints for modular organisation:

Blueprint	URL Prefix	Responsibility
auth	/auth	Registration, login, logout, access control
blog	/ (root)	Post CRUD, listing, author verification

3. Database Layer

Function	Purpose
get_db()	Returns request-scoped SQLite connection via Flask's g object
close_db()	Teardown handler — closes connection at end of request
init_db()	Executes schema.sql to create tables
init_db_command()	CLI: flask init-db

Schema:

CREATE TABLE user (
    id       INTEGER PRIMARY KEY AUTOINCREMENT,
    username TEXT UNIQUE NOT NULL,
    password TEXT        NOT NULL
);

CREATE TABLE post (
    id        INTEGER PRIMARY KEY AUTOINCREMENT,
    author_id INTEGER   NOT NULL,
    created   TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
    title     TEXT      NOT NULL,
    body      TEXT      NOT NULL,
    FOREIGN KEY (author_id) REFERENCES user (id)
);

4. Authentication Flow

• Registration → Validate input → Hash password (PBKDF2) → Insert user
• Login → Verify credentials → Store user_id in signed session cookie
• Per-request → load_logged_in_user() runs before every request, loads g.user from session
• Access control → @login_required decorator redirects unauthenticated users

5. Request Lifecycle

Example: User creates a new blog post.

1. Browser sends GET /create
2. load_logged_in_user() fires → loads user from session into g.user
3. @login_required checks g.user → redirects to login if missing
4. create() renders the form template
5. User submits POST /create with form data
6. View validates input → inserts post with g.user['id'] as author → commits
7. close_db() teardown closes the SQLite connection
8. Redirect to index

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Key Design Patterns

Pattern	Implementation
Application Factory	create_app() creates configured Flask instance
Blueprint	Modular route organisation (auth, blog)
Request Context	g.user, g.db — per-request data, auto-cleaned
Session Management	Signed cookies, session['user_id']
Decorator	@login_required, @bp.before_app_request
Template Inheritance	base.html → child templates extend blocks

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Screenshots

Coming soon

Screenshots of the blog interface will be added here.