如何获取字符串列的sqlalchemy长度

from sqlalchemy import Column, String

# 创建表
class MyTable(Base):
    __tablename__ = 'mytable'

    id = Column(Integer, primary_key=True)
    name = Column(String)

# 创建数据库连接
engine = create_engine('sqlite:///mytable.db')
Base.metadata.create_all(engine)

# 插入数据
Session = sessionmaker(bind=engine)
session = Session()

my_data = {'name': 'John Doe'}
session.add(MyTable(**my_data))
session.commit()

# 获取字符串列的长度
result = session.query(MyTable).filter_by(name=my_data['name']).first()
print(result.name.length())

from sqlalchemy import Column, Unicode

# 创建表
class MyTable(Base):
    __tablename__ = 'mytable'

    id = Column(Integer, primary_key=True)
    name = Column(Unicode)

# 创建数据库连接
engine = create_engine('sqlite:///mytable.db')
Base.metadata.create_all(engine)

# 插入数据
Session = sessionmaker(bind=engine)
session = Session()

my_data = {'name': 'John Doe'}
session.add(MyTable(**my_data))
session.commit()

# 获取字符串列的长度
result = session.query(MyTable).filter_by(name=my_data['name']).first()
print(result.name.length())