initial

backend/app/db.py

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+"""Database engine + session factory."""
+from __future__ import annotations
+
+from contextlib import asynccontextmanager
+from typing import AsyncIterator
+
+from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
+from sqlalchemy.orm import DeclarativeBase
+
+from app.config import settings
+
+
+class Base(DeclarativeBase):
+    pass
+
+
+_engine_kwargs: dict = dict(
+    echo=False,
+    pool_pre_ping=True,
+)
+# Pool size params only for Postgres/MySQL (not SQLite)
+if "sqlite" not in settings.database_url:
+    _engine_kwargs.update(pool_size=10, max_overflow=20)
+
+engine = create_async_engine(settings.database_url, **_engine_kwargs)
+
+AsyncSessionLocal = async_sessionmaker(
+    engine, class_=AsyncSession, expire_on_commit=False, autoflush=False
+)
+
+
+@asynccontextmanager
+async def get_db() -> AsyncIterator[AsyncSession]:
+    async with AsyncSessionLocal() as session:
+        try:
+            yield session
+            await session.commit()
+        except Exception:
+            await session.rollback()
+            raise
+
+
+async def get_db_dep() -> AsyncIterator[AsyncSession]:
+    """FastAPI dependency."""
+    async with AsyncSessionLocal() as session:
+        try:
+            yield session
+        finally:
+            await session.close()