"""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