old_contents: import datetime
  
  from sqlalchemy.schema import Column
  from sqlalchemy.types import DateTime, Integer
  
  from sqlalchemy.ext.declarative import declarative_base, declared_attr
  
  
  Base = declarative_base()
  
  
  class BaseMixin:
  
      id = Column(Integer, primary_key=True)
  
      @declared_attr
      def __tablename__(cls):
          return cls.__name__.lower()
  
  
  class TimestampMixin:
  
      created_at = Column(
          DateTime, nullable=False, default=datetime.datetime.now)
      updated_at = Column(DateTime)
  
new_contents: from datetime import datetime
  
  from sqlalchemy.schema import Column
  from sqlalchemy.types import DateTime, Integer
  
  from sqlalchemy.ext.declarative import declarative_base, declared_attr
  
  
  Base = declarative_base()
  
  
  class BaseMixin:
  
      id = Column(Integer, primary_key=True)
  
      @declared_attr
      def __tablename__(cls):
          return cls.__name__.lower()
  
  
  class TimestampMixin:
  
      created_at = Column(DateTime, nullable=False, default=datetime.now)
      updated_at = Column(DateTime, onupdate=datetime.now)
  
subject: Update updated time on update