old_contents: from sqlalchemy import Table, Column, Integer, String, DateTime, ForeignKey
  from sqlalchemy.orm import relationship
  from sqlalchemy.sql import func
  from sqlalchemy.ext.declarative import declared_attr, declarative_base
  
  from chatterbot.conversation import StatementMixin
  from chatterbot import constants
  
  
  class ModelBase(object):
      """
      An augmented base class for SqlAlchemy models.
      """
  
      @declared_attr
      def __tablename__(cls):
          """
          Return the lowercase class name as the name of the table.
          """
          return cls.__name__.lower()
  
      id = Column(
          Integer,
          primary_key=True,
          autoincrement=True
      )
  
  
  Base = declarative_base(cls=ModelBase)
  
  
  tag_association_table = Table(
      'tag_association',
      Base.metadata,
      Column('tag_id', Integer, ForeignKey('tag.id')),
      Column('statement_id', Integer, ForeignKey('statement.id'))
  )
  
  
  class Tag(Base):
      """
      A tag that describes a statement.
      """
  
      name = Column(
          String(constants.TAG_NAME_MAX_LENGTH)
      )
  
  
  class Statement(Base, StatementMixin):
      """
      A Statement represents a sentence or phrase.
      """
  
      text = Column(
          String(constants.STATEMENT_TEXT_MAX_LENGTH)
      )
  
      conversation = Column(
          String(constants.CONVERSATION_LABEL_MAX_LENGTH)
      )
  
      created_at = Column(
          DateTime(timezone=True),
          server_default=func.now()
      )
  
      tags = relationship(
          'Tag',
          secondary=lambda: tag_association_table,
          backref='statements'
      )
  
      in_response_to = Column(
          String(constants.STATEMENT_TEXT_MAX_LENGTH),
          nullable=True
      )
  
      persona = Column(
          String(constants.PERSONA_MAX_LENGTH)
      )
  
      def get_tags(self):
          """
          Return a list of tags for this statement.
          """
          return [tag.name for tag in self.tags]
  
new_contents: from sqlalchemy import Table, Column, Integer, String, DateTime, ForeignKey
  from sqlalchemy.orm import relationship
  from sqlalchemy.sql import func
  from sqlalchemy.ext.declarative import declared_attr, declarative_base
  
  from chatterbot.conversation import StatementMixin
  from chatterbot import constants
  
  
  class ModelBase(object):
      """
      An augmented base class for SqlAlchemy models.
      """
  
      @declared_attr
      def __tablename__(cls):
          """
          Return the lowercase class name as the name of the table.
          """
          return cls.__name__.lower()
  
      id = Column(
          Integer,
          primary_key=True,
          autoincrement=True
      )
  
  
  Base = declarative_base(cls=ModelBase)
  
  
  tag_association_table = Table(
      'tag_association',
      Base.metadata,
      Column('tag_id', Integer, ForeignKey('tag.id')),
      Column('statement_id', Integer, ForeignKey('statement.id'))
  )
  
  
  class Tag(Base):
      """
      A tag that describes a statement.
      """
  
      name = Column(
          String(constants.TAG_NAME_MAX_LENGTH)
      )
  
  
  class Statement(Base, StatementMixin):
      """
      A Statement represents a sentence or phrase.
      """
  
      text = Column(
          String(constants.STATEMENT_TEXT_MAX_LENGTH)
      )
  
      conversation = Column(
          String(constants.CONVERSATION_LABEL_MAX_LENGTH),
          nullable=False,
          server_default=''
      )
  
      created_at = Column(
          DateTime(timezone=True),
          server_default=func.now()
      )
  
      tags = relationship(
          'Tag',
          secondary=lambda: tag_association_table,
          backref='statements'
      )
  
      in_response_to = Column(
          String(constants.STATEMENT_TEXT_MAX_LENGTH),
          nullable=True
      )
  
      persona = Column(
          String(constants.PERSONA_MAX_LENGTH),
          nullable=False,
          server_default=''
      )
  
      def get_tags(self):
          """
          Return a list of tags for this statement.
          """
          return [tag.name for tag in self.tags]
  
subject: Set defaults for SQL Alchemy columns