modify the project, everything go under app folder

app/models/message.py

@@ -0,0 +1,11 @@
+from sqlalchemy import Column, DateTime, String, ForeignKey
+from sqlalchemy.sql import func
+from .base import Base, AutoID
+
+class Message(Base, AutoID):
+    __tablename__ = "messages"
+
+    user_id = Column(String, ForeignKey("users.id"), index=True)
+    content = Column(String)
+
+    created_at = Column(DateTime(timezone=True), server_default=func.now())