first commit

backend/app/db.py

@@ -0,0 +1,20 @@
+"""async SQLAlchemy 引擎与会话。"""
+from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
+from sqlalchemy.orm import DeclarativeBase
+
+from .config import settings
+
+
+class Base(DeclarativeBase):
+    """所有 ORM 模型的基类。"""
+
+
+# echo=False；生产环境可用连接池参数调优
+engine = create_async_engine(settings.database_url, echo=False, future=True)
+async_session = async_sessionmaker(engine, expire_on_commit=False, class_=AsyncSession)
+
+
+async def get_session() -> AsyncSession:
+    """FastAPI 依赖：提供一个事务会话。"""
+    async with async_session() as session:
+        yield session