我想你的 Base 班级混音 name 列？
你的目标是 inspect(category).committed_state 看起来就像新创建的对象一样（除了 id 属性）。每个产品对象都一样。
在“新建对象”示例中， category 的 committed_state 在刷新会话之前如下所示：

{'id': symbol('NEVER_SET'),
 'name': symbol('NO_VALUE'),
 'products': [],
 'top_product': symbol('NEVER_SET')}

而 product 的 committed_state 看起来像这样：

{'category': symbol('NEVER_SET'),
 'id': symbol('NEVER_SET'),
 'name': symbol('NO_VALUE')}

要获得更新后的行为，需要两者都过期 category.top_product_id （以防止其被纳入 INSERT )还有软糖 category.top_product 的 committed_state （为了使sqlalchemy相信值已经改变，因此需要引起 UPDATE ).
首先，过期 category.top_product_id 制作前 category transient ：

source_session.expire(category, ["top_product_id"])

然后是软糖 category.top_product 的 committed_state （这可能发生在 category transient ）：

from sqlalchemy import inspect
from sqlalchemy.orm.base import NEVER_SET
inspect(category).committed_state.update(top_product=NEVER_SET)

完整示例：

from sqlalchemy import Column, ForeignKey, Integer, String, create_engine, inspect
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import Session, make_transient, relationship
from sqlalchemy.orm.base import NEVER_SET

class Base(object):
    name = Column(String(50), nullable=False)

Base = declarative_base(cls=Base)

class Category(Base):
    __tablename__ = 'categories'
    id = Column(Integer, primary_key=True)
    top_product_id = Column(Integer, ForeignKey('products.id'))
    products = relationship('Product', primaryjoin='Product.category_id == Category.id', back_populates='category', cascade='all', lazy='selectin')
    top_product = relationship('Product', primaryjoin='Category.top_product_id == Product.id', post_update=True, cascade='all', lazy='selectin')

class Product(Base):
    __tablename__ = 'products'
    id = Column(Integer, primary_key=True)
    category_id = Column(Integer, ForeignKey('categories.id'), nullable=False)
    category = relationship('Category', primaryjoin='Product.category_id == Category.id', back_populates='products', cascade='all', lazy='selectin')

source_engine = create_engine('sqlite:///')
dest_engine = create_engine('sqlite:///', echo=True)

def fk_pragma_on_connect(dbapi_con, con_record):
    dbapi_con.execute('pragma foreign_keys=ON')

from sqlalchemy import event
for engine in [source_engine, dest_engine]:
    event.listen(engine, 'connect', fk_pragma_on_connect)

Base.metadata.create_all(bind=source_engine)
Base.metadata.create_all(bind=dest_engine)

source_session = Session(bind=source_engine)
dest_session = Session(bind=dest_engine)

source_category = Category(id=99, name='SomeCategoryName')
source_product = Product(category=source_category, id=100, name='SomeProductName')
source_category.top_product = source_product
source_session.add(source_category)
source_session.commit()
source_session.close()

# If you want to test UPSERTs in dest_session.

# dest_category = Category(id=99, name='PrevCategoryName')

# dest_product = Product(category=dest_category, id=100, name='PrevProductName')

# dest_category.top_product = dest_product

# dest_session.add(dest_category)

# dest_session.commit()

# dest_session.close()

category = source_session.query(Category).filter(Category.id == 99).one()

# Ensure relationship attributes are initialized before we make objects transient.

_ = category.top_product

# source_session.expire(category, ['id'])  # only if you want new IDs in dest_session

source_session.expire(category, ['top_product_id'])
for product in category.products:
    # Ensure relationship attributes are initialized before we make objects transient.
    _ = product.category
    # source_session.expire(product, ['id'])  # only if you want new IDs in dest_session
    # Not strictly needed as long as Product.category is not a post-update relationship.
    source_session.expire(product, ['category_id'])

make_transient(category)
inspect(category).committed_state.update(top_product=NEVER_SET)

for product in category.products:
    make_transient(product)
    # Not strictly needed as long as Product.category is not a post-update relationship.
    inspect(product).committed_state.update(category=NEVER_SET)

dest_session.add(category)

# Or, if you want UPSERT (must retain original IDs in this case)

# dest_session.merge(category)

dest_session.flush()

产生了这个dml dest_session :

INSERT INTO categories (name, id, top_product_id) VALUES (?, ?, ?)
('SomeCategoryName', 99, None)
INSERT INTO products (name, id, category_id) VALUES (?, ?, ?)
('SomeProductName', 100, 99)
UPDATE categories SET top_product_id=? WHERE categories.id = ?
(100, 99)

好像 make_transient 应该重置 committed_state 好像它是一个新的物体，但我猜不是。