app/db.py

import os
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker, DeclarativeBase


DATABASE_URL = os.getenv("DATABASE_URL", "sqlite:///./app.db")


class Base(DeclarativeBase):
    pass


if DATABASE_URL.startswith("sqlite"):
    engine = create_engine(
        DATABASE_URL,
        connect_args={"check_same_thread": False},
    )
else:
    engine = create_engine(
        DATABASE_URL,
        pool_pre_ping=True,   # validate connections before use to avoid stale sockets
        pool_recycle=280,     # recycle before Neon's ~5 min idle timeout
        pool_size=5,
        max_overflow=10,
    )

SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)


def get_db():
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()