fix bugs for launch: postgresql url for sqlalchemy; auto loading env

app/db.py

@@ -1,8 +1,22 @@
 import os
 from sqlalchemy import create_engine
 from sqlalchemy.orm import sessionmaker
+from dotenv import load_dotenv
+
+# 加载 .env 文件
+load_dotenv()
 
 DATABASE_URL = os.getenv("DATABASE_URL")
 
+#  自动将旧版的 postgres:// 替换为 SQLAlchemy 强要求的 postgresql://
+if DATABASE_URL and DATABASE_URL.startswith("postgres://"):
+    DATABASE_URL = DATABASE_URL.replace("postgres://", "postgresql://", 1)
+elif DATABASE_URL and DATABASE_URL.startswith("postgres+"):
+    DATABASE_URL = DATABASE_URL.replace("postgres+", "postgresql+", 1)
+
+# 如果环境变量彻底缺失，做一个安全的报错提示
+if not DATABASE_URL:
+    raise ValueError("DATABASE_URL environment variable is not set or empty.")
+
 engine = create_engine(DATABASE_URL)
 SessionLocal = sessionmaker(bind=engine)