fix: use kwargs registry directly and store it in model_config

In SQLModelMetaclass.__new__, the registry configuration block had two bugs:

1. config_registry was sourced via get_config("registry"), which reads the
   inherited model_config first. Once any parent class sets model_config["registry"]
   (as SQLModel itself does), subclasses that pass a custom registry=... kwarg
   would silently get the parent's registry instead of their own.

2. model_config["registry"] was assigned config_table (a copy-paste error)
   instead of config_registry, so the model_config entry always ended up as
   PydanticUndefined rather than the actual registry object.

Fix both by reading directly from kwargs (honoring the kwarg for the class being
defined without inheriting an ancestor's value) and writing the correct variable.

Reproducer:
    custom_registry = registry()
    class MyBase(SQLModel, registry=custom_registry): pass
    # Before: MyBase.model_config["registry"] == PydanticUndefined
    # After:  MyBase.model_config["registry"] is custom_registry

Author: JSap0914

sqlmodel/main.py

@@ -613,11 +613,11 @@ def get_config(name: str) -> Any:
             # TODO: remove this in the future
             new_cls.model_config["read_with_orm_mode"] = True  # ty: ignore[invalid-key]
 
-        config_registry = get_config("registry")
+        config_registry = kwargs.get("registry", Undefined)
         if config_registry is not Undefined:
             config_registry = cast(registry, config_registry)
             # If it was passed by kwargs, ensure it's also set in config
-            new_cls.model_config["registry"] = config_table
+            new_cls.model_config["registry"] = config_registry
             setattr(new_cls, "_sa_registry", config_registry)  # noqa: B010
             setattr(new_cls, "metadata", config_registry.metadata)  # noqa: B010
             setattr(new_cls, "__abstract__", True)  # noqa: B010

tests/test_registry_kwarg.py

@@ -0,0 +1,30 @@
+"""Tests for SQLModelMetaclass.__new__ registry kwarg handling."""
+import pytest
+from sqlalchemy.orm import registry
+from sqlmodel import SQLModel
+
+
+def test_custom_registry_base_stores_registry_in_model_config() -> None:
+    """model_config['registry'] must hold the registry object passed as kwarg."""
+    custom_registry = registry()
+
+    class MyBase(SQLModel, registry=custom_registry):
+        pass
+
+    stored = MyBase.model_config.get("registry")
+    assert stored is custom_registry, (
+        f"model_config['registry'] should be the custom registry, got {stored!r}"
+    )
+
+
+def test_custom_registry_base_sets_sa_registry() -> None:
+    """_sa_registry must reference the registry object passed as kwarg."""
+    custom_registry = registry()
+
+    class MyBase2(SQLModel, registry=custom_registry):
+        pass
+
+    sa_registry = getattr(MyBase2, "_sa_registry", None)
+    assert sa_registry is custom_registry, (
+        f"_sa_registry should be the custom registry, got {sa_registry!r}"
+    )