MarshmallowSqlAlchemy's issue with overriden ids not being serialized

marshmallow_sa_inherit_pk.py

import sqlalchemy as sa
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import scoped_session, sessionmaker, relationship
from sqlalchemy.ext.hybrid import hybrid_property
from marshmallow_sqlalchemy import ModelSchema

engine = sa.create_engine('sqlite:///:memory:')
session = scoped_session(sessionmaker(bind=engine))
Base = declarative_base()

class Person(Base):
    __tablename__ = 'person'

    type = sa.Column(sa.String(50))
    __mapper_args__ = {
        'polymorphic_identity': 'person',
        'polymorphic_on': type
    }

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


    def __repr__(self):
        return '<Person(name={self.name!r})>'.format(self=self)


class Author(Person):
    __tablename__ = 'authors'

    __mapper_args__ = {
        'polymorphic_identity': 'author'
    }

    id = sa.Column(sa.Integer, sa.ForeignKey('person.id'), primary_key=True)


    featured = sa.Column(sa.Boolean)


    def __repr__(self):
        return '<Author(name={self.name!r})>'.format(self=self)


class Book(Base):
    __tablename__ = 'books'

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

    author_id = sa.Column(sa.Integer, sa.ForeignKey('authors.id'))
    author = relationship('Author', backref='books')


Base.metadata.create_all(engine)


class PersonSchema(ModelSchema):
    class Meta:
        model = Person
        sqla_session = session


class AuthorSchema(ModelSchema):
    class Meta:
        model = Author
        sqla_session = session


class BookSchema(ModelSchema):
    class Meta:
        model = Book
        sqla_session = session

person_schema = PersonSchema()
author_schema = AuthorSchema()
book_schema = BookSchema()

author = Author(name='Chuck Paluhniuk')
# person = Person(name='Chuck Paluhniuk')
session.add(author)
# session.add(person)

book = Book(name='SomeBook', author=author)
session.add(book)

session.commit()

print
data_dump = author_schema.dump(author).data
print data_dump

data_dump = person_schema.dump(author).data
print data_dump

# data, error = author_schema.load(data_dump)