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

Problem

You have a sqlmodel set of models such as

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")

But when you try to create one of these models, you get an error like

  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.

Solution

The issue here is that you have specified in Product that it has a relationship to Offer with back_populates="products", but that column (products) doesn’t exist in Offer.

To fix this, you need to make sure that the back_populates argument in the Relationship is set to the correct column name in the other model, or create it:

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
    )

The column needs to be spelled exactly as it is in the other model, so double-check if that’s the case.

Alternatively, you can remove the back_populates argument from the Relationship if you don’t need it.