feat: T03+T04 backend - FastAPI, DB models, Rentman integration, admin auth, APScheduler

backend/app/database.py

@@ -0,0 +1,42 @@
+"""SQLAlchemy async database engine and session."""
+from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
+from sqlalchemy.orm import DeclarativeBase
+from app.config import get_settings
+
+
+class Base(DeclarativeBase):
+    """Declarative base for all models."""
+    pass
+
+
+settings = get_settings()
+
+engine = create_async_engine(
+    settings.database_url,
+    echo=False,
+    pool_pre_ping=True,
+)
+
+async_session = async_sessionmaker(
+    engine,
+    class_=AsyncSession,
+    expire_on_commit=False,
+)
+
+
+async def get_db() -> AsyncSession:
+    """Dependency: yield an async database session."""
+    async with async_session() as session:
+        try:
+            yield session
+        except Exception:
+            await session.rollback()
+            raise
+        finally:
+            await session.close()
+
+
+async def init_db() -> None:
+    """Create all tables (for testing / first run)."""
+    async with engine.begin() as conn:
+        await conn.run_sync(Base.metadata.create_all)