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如何修复 sqlmodel InvalidRequestError: Mapper 'Mapper[...]' has no property '...'. If this property was indicated from other mappers or configure events, ensure registry.configure() has been called.

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问题

你有一组 sqlmodel 模型如

sqlmodel_invalidrequest_example.py

class Offer(SQLModel, table=True):
    id: Optional[int] = Field(default=None, primary_key=True)
    # ...

class Product(SQLModel, table=True):
    id: Optional[int] = Field(default=None, primary_key=True)
    # ...
    offers: List[Offer] = Relationship(
        back_populates="products",
        link_model=ProductOfferLink
    )

class ProductOfferLink(SQLModel, table=True):
    id: Optional[int] = Field(default=None, primary_key=True)
    product_id: int = Field(foreign_key="product.id")
    offer_id: int = Field(foreign_key="offer.id")

但当你尝试创建这些模型之一时，你得到如下错误

sqlalchemy_error_log.txt
  File "/home/uli/.local/lib/python3.12/site-packages/sqlalchemy/orm/state.py", line 566, in _initialize_instance
    manager.dispatch.init(self, args, kwargs)
  File "/home/uli/.local/lib/python3.12/site-packages/sqlalchemy/event/attr.py", line 497, in __call__
    fn(*args, **kw)
  File "/home/uli/.local/lib/python3.12/site-packages/sqlalchemy/orm/mapper.py", line 4396, in _event_on_init
    instrumenting_mapper._check_configure()
  File "/home/uli/.local/lib/python3.12/site-packages/sqlalchemy/orm/mapper.py", line 2388, in _check_configure
    _configure_registries({self.registry}, cascade=True)
  File "/home/uli/.local/lib/python3.12/site-packages/sqlalchemy/orm/mapper.py", line 4204, in _configure_registries
    _do_configure_registries(registries, cascade)
  File "/home/uli/.local/lib/python3.12/site-packages/sqlalchemy/orm/mapper.py", line 4245, in _do_configure_registries
    mapper._post_configure_properties()
  File "/home/uli/.local/lib/python3.12/site-packages/sqlalchemy/orm/mapper.py", line 2405, in _post_configure_properties
    prop.init()
  File "/home/uli/.local/lib/python3.12/site-packages/sqlalchemy/orm/interfaces.py", line 584, in init
    self.do_init()
  File "/home/uli/.local/lib/python3.12/site-packages/sqlalchemy/orm/relationships.py", line 1647, in do_init
    self._generate_backref()
  File "/home/uli/.local/lib/python3.12/site-packages/sqlalchemy/orm/relationships.py", line 2133, in _generate_backref
    self._add_reverse_property(self.back_populates)
  File "/home/uli/.local/lib/python3.12/site-packages/sqlalchemy/orm/relationships.py", line 1578, in _add_reverse_property
    other = self.mapper.get_property(key, _configure_mappers=False)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/uli/.local/lib/python3.12/site-packages/sqlalchemy/orm/mapper.py", line 2511, in get_property
    raise sa_exc.InvalidRequestError(
sqlalchemy.exc.InvalidRequestError: Mapper 'Mapper[Offer(offer)]' has no property 'product'.  If this property was indicated from other mappers or configure events, ensure registry.configure() has been called.

解决方案

这里的问题是你已在 Product 中指定它与 Offer 有关系，使用 back_populates="products"，但该列（products）在 Offer 中不存在。

要修复此问题，你需要确保 Relationship 中的 back_populates 参数设置为另一个模型中正确的列名，或创建它：

sqlmodel_relationship_fix.py

class Offer(SQLModel, table=True):
    id: Optional[int] = Field(default=None, primary_key=True)
    # ...
    # Add this line to fix the issue
    products: List["Product"] = Relationship(
        back_populates="offers",
        link_model=ProductCategoryLink
    )

该列需要与另一个模型中的拼写完全一致，所以请仔细检查是否如此。

或者，如果你不需要 back_populates 参数，可以从 Relationship 中删除它。

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