需要用于SqlAlchemy单表继承的经典映射器示例

from sqlalchemy import Column, Integer, String
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship

Base = declarative_base()

class Animal(Base):
    __tablename__ = 'animals'
    id = Column(Integer, primary_key=True)
    type = Column(String(50))
    name = Column(String(50))

    __mapper_args__ = {
        'polymorphic_on': type,
        'polymorphic_identity': 'animal'
    }

class Dog(Animal):
    __tablename__ = 'dogs'
    id = Column(Integer, primary_key=True)
    breed = Column(String(50))

    __mapper_args__ = {
        'polymorphic_identity': 'dog'
    }

class Cat(Animal):
    __tablename__ = 'cats'
    id = Column(Integer, primary_key=True)
    color = Column(String(50))

    __mapper_args__ = {
        'polymorphic_identity': 'cat'
    }

from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker

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

dog = Dog(name='Buddy', breed='Labrador Retriever')
cat = Cat(name='Kitty', color='Calico')

session.add(dog)
session.add(cat)
session.commit()

animals = session.query(Animal).all()
for animal in animals:
    print(animal.name)