Help: Model Inheritance Not Working

[oxxzz]

My idea is that some fields exist in all tables, such as: creation time, update time, deletion time, etc. I want to achieve coding efficiency through model class inheritance. But I got the following error: pony.orm.core.ERDiagramError: Base Entity does not belong to any database.

Please help me see or give some suggestions, thank you very much!

# main.py

from pony import orm
from datetime import datetime

orm.set_sql_debug(True)
db = orm.Database()
db.bind(
    provider='mysql', 
    host='127.0.0.1', 
    user='root', 
    passwd='secret', 
    db='demo'
)

class Entity(db.Entity):
    created_at = orm.Optional(datetime)
    updated_at = orm.Optional(datetime)

class Podcast(Entity):
    _table_ = "podcasts"
    id = orm.PrimaryKey(int, auto=True)
    bid = orm.Required(int)
    title = orm.Required(str)
    cover = orm.Optional(str)
    sequence = orm.Optional(int)

db.generate_mapping(create_tables=False, check_tables=False)

with orm.db_session as s:
    p = Podcast[1]
    print(p)

$ uv run main.py
================ ERROR ================

GET NEW CONNECTION
RELEASE CONNECTION
Traceback (most recent call last):
  File "/fake/dir/main.py", line 17, in <module>
    class Podcast(Entity):
  File "/fake/dir/.venv/lib/python3.12/site-packages/pony/orm/core.py", line 3700, in __init__
    if database is None: throw(ERDiagramError, 'Base Entity does not belong to any database')
                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/fake/dir/.venv/lib/python3.12/site-packages/pony/utils/utils.py", line 99, in throw
    raise exc
pony.orm.core.ERDiagramError: Base Entity does not belong to any database