FastAPI PostgreSQL Code Audit

Code Review Overview

This comprehensive audit evaluates a FastAPI application with PostgreSQL backend against industry best practices for production-grade systems. The review covers 8 critical dimensions with severity-rated findings and actionable recommendations.

Code Structure

Modularity, dependency injection, and logical organization of components.

Database Layer

Connection management, async operations, query optimization, and migrations.

API Security

Authentication, validation, CORS, rate limiting, and HTTPS enforcement.

Error Handling

Comprehensive error management, logging, and status codes.

Detailed Audit Findings

Code Structure & Organization

High: Monolithic Structure Detected

The application lacks proper modularization with all routes in a single file. Consider implementing FastAPI routers:

# Recommended structure:
app/
├── api/
│   ├── v1/
│   │   ├── endpoints/
│   │   │   ├── users.py
│   │   │   ├── items.py
│   │   ├── __init__.py
│   ├── __init__.py
├── models/
├── schemas/
├── services/

Medium: Inconsistent Dependency Injection

Mix of direct instantiation and dependency injection found. Standardize on FastAPI's Depends():

# Instead of:
def get_db():
    return SessionLocal()

# Use:
async def get_db() -> AsyncSession:
    async with AsyncSessionLocal() as session:
        yield session

# Then in routes:
@app.get("/items/")
async def read_items(db: AsyncSession = Depends(get_db)):
    ...

Database Layer Best Practices

Critical: Connection Leak Risk

Database connections are not properly managed in async context. Implement connection pooling with asyncpg:

# Recommended approach:
from asyncpg import create_pool

async def get_db_pool():
    return await create_pool(
        user="user",
        password="password",
        database="dbname",
        host="localhost",
        min_size=5,
        max_size=20
    )

# In FastAPI startup:
@app.on_event("startup")
async def startup():
    app.state.db_pool = await get_db_pool()

@app.on_event("shutdown")
async def shutdown():
    await app.state.db_pool.close()

Medium: Missing Indexes on Frequent Queries

Common query patterns lack proper indexing. Analyze slow queries and add appropriate indexes:

-- Example for user queries:
CREATE INDEX idx_users_email ON users(email);
CREATE INDEX idx_users_created_at ON users(created_at);

-- Composite index for common filters:
CREATE INDEX idx_items_status_category ON items(status, category);

API Design & Security

High: Insecure Authentication Implementation

Basic auth found in production. Implement OAuth2 with JWT tokens:

# Recommended security setup:
from fastapi.security import OAuth2PasswordBearer

oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token")

async def get_current_user(
    token: str = Depends(oauth2_scheme),
    db: Session = Depends(get_db)
):
    credentials_exception = HTTPException(
        status_code=401,
        detail="Invalid credentials"
    )
    try:
        payload = jwt.decode(token, SECRET_KEY, algorithms=[ALGORITHM])
        username: str = payload.get("sub")
        if username is None:
            raise credentials_exception
    except JWTError:
        raise credentials_exception
    
    user = db.get_user(username)
    if user is None:
        raise credentials_exception
    return user

Medium: Missing Rate Limiting

API endpoints lack protection against brute force attacks. Implement rate limiting:

# Using slowapi for rate limiting:
from slowapi import Limiter
from slowapi.util import get_remote_address

limiter = Limiter(key_func=get_remote_address)
app.state.limiter = limiter

@app.post("/login")
@limiter.limit("5/minute")
async def login(request: Request, user_data: UserLogin):
    ...