如何在sqlalchemy中将Dict[str，str]用作关系属性

from sqlalchemy import Column, Integer, String, create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker
from sqlalchemy.types import TypeDecorator, VARCHAR
import json

class DictType(TypeDecorator):
    impl = VARCHAR

    def process_bind_param(self, value, dialect):
        if value is not None:
            value = json.dumps(value)
        return value

    def process_result_value(self, value, dialect):
        if value is not None:
            value = json.loads(value)
        return value

Base = declarative_base()

class MyModel(Base):
    __tablename__ = 'mymodel'

    id = Column(Integer, primary_key=True)
    data = Column(DictType)

engine = create_engine('sqlite:///mydatabase.db')
Base.metadata.create_all(engine)
Session = sessionmaker(bind=engine)
session = Session()

data = {'key1': 'value1', 'key2': 'value2'}
model = MyModel(data=data)

session.add(model)
session.commit()

result = session.query(MyModel).filter_by(id=1).first()
print(result.data)  # {'key1': 'value1', 'key2': 'value2'}