袁聪的第一次提交，包含nl2sql,行情数据,场外申购

app/infrastructure/db.py

@@ -1,6 +1,12 @@
 from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
+from sqlalchemy.pool import NullPool
 
 from app.core.config import get_settings
 
-engine = create_async_engine(get_settings().mysql_dsn, pool_pre_ping=True)
+settings = get_settings()
+engine = create_async_engine(
+    settings.mysql_dsn,
+    pool_pre_ping=settings.mysql_pool_pre_ping,
+    poolclass=NullPool,
+)
 SessionFactory = async_sessionmaker(engine, class_=AsyncSession, expire_on_commit=False)