fix issue with widget assignment for custom ForeignKey subclasses (#1826

)

* fix issue with widget assignment for custom ForeignKey subclasses

* updated changelog

docs/changelog.rst

@@ -5,13 +5,14 @@ Changelog
 
     Version 4 introduces breaking changes.  Please refer to :doc:`release notes<release_notes>`.
 
-4.0.2 (unreleased)
+4.0.2 (2024-05-13)
 ------------------
 
 - fix export with custom column name (`1821 <https://github.com/django-import-export/django-import-export/pull/1821>`_)
 - fix allow ``column_name`` to be declared in ``fields`` list (`1822 <https://github.com/django-import-export/django-import-export/pull/1822>`_)
 - fix clash between ``key_is_id`` and ``use_natural_foreign_keys`` (`1824 <https://github.com/django-import-export/django-import-export/pull/1824>`_)
 - remove unreachable code (`1825 <https://github.com/django-import-export/django-import-export/pull/1825>`_)
+- fix issue with widget assignment for custom ``ForeignKey`` subclasses (`1826 <https://github.com/django-import-export/django-import-export/pull/1826>`_)
 
 4.0.1 (2024-05-08)
 ------------------

import_export/resources.py

@@ -1264,6 +1264,8 @@ def widget_from_django_field(cls, f, default=widgets.Widget):
             for base_class in inspect.getmro(f.__class__):
                 if base_class.__name__ in cls.WIDGETS_MAP:
                     result = cls.WIDGETS_MAP[base_class.__name__]
+                    if isinstance(result, str):
+                        result = getattr(cls, result)(f)
                     break
 
             try:

tests/core/tests/test_model_resource_fields_generate_widgets.py

@@ -7,10 +7,11 @@
 from django.contrib.postgres import search as postgres_search
 from django.contrib.postgres.fields import ranges as postgres_ranges
 from django.db import models
-from django.db.models.fields.related import RelatedField
+from django.db.models.fields.related import ForeignKey, RelatedField
 
 from import_export import widgets
 from import_export.resources import ModelResource
+from import_export.widgets import ForeignKeyWidget
 
 
 class ExampleResource(ModelResource):
@@ -188,3 +189,22 @@ def _get_django_fields_for_check_widget(self):
             postgres.RangeField(),
         ]
         return fields
+
+    def test_custom_fk_field(self):
+        # issue 1817 - if a 'custom' foreign key field is provided, then this should
+        # be handled when widgets are defined
+        class CustomForeignKey(ForeignKey):
+            def __init__(
+                self,
+                to,
+                on_delete,
+                **kwargs,
+            ):
+                super().__init__(to, on_delete, **kwargs)
+
+        resource_field = ModelResource.field_from_django_field(
+            "custom_fk",
+            CustomForeignKey(WithPositiveIntegerFields, on_delete=models.SET_NULL),
+            False,
+        )
+        self.assertEqual(ForeignKeyWidget, resource_field.widget.__class__)