SQLAlchemy多形性_标识不起作用

我正在尝试在具有多个继承的python类上使用多态性:

engine = create_engine(
    'mysql://xxx:yyy@localhost:3306/zzz?charset=utf8&use_unicode=0',
    pool_recycle=3600, echo=True)

Base = declarative_base()

class AbstractPersistent(object):
    version = Column('VERSION', Integer)
    last_modified_by = Column('LAST_MODIFIED_BY', String(255))
    last_modified_date = Column('LAST_MODIFIED_DATE', Date)
    created_by = Column('CREATED_BY', String(255))
    created_date = Column('CREATED_DATE', Date)

class AbstractNamed(AbstractPersistent):
    eid = Column('ENTERPRISE_ID', String(255))
    title = Column('TITLE', String(255))
    description = Column('DESCRIPTION', String(255))

class AbstractContainer(AbstractNamed):
    __tablename__ = 'CM_MEMBER_CONTAINER_T'    
    id = Column('MEMBER_CONTAINER_ID',Integer,primary_key=True)
    discriminator = Column('CLASS_DISCR', String(100))
    __mapper_args__ = {'polymorphic_on': discriminator }

class CourseSet(Base,AbstractContainer):
    __mapper_args__ = {'polymorphic_identity': 'org.sakaiproject.coursemanagement.impl.CourseSetCmImpl'}

正如你所看到的, CourseSet 包含其父级的所有列并具有该列 CLASS_DISCR 集合到 'org.sakaiproject.coursemanagement.impl.CourseSetCmImpl' .

但当它对所有 法庭 :

Session = sessionmaker(bind=engine)
session = Session()
course_sets = session.query(CourseSet).all()
print(course_sets)

它返回 'CM_MEMBER_CONTAINER_T' 但是我只想要那些 类别分类 设置为 'org.sakaiproject.coursemanagement.impl.coursesetcmimpl'

有什么想法吗?