Allow single generic param for Field in ForeignKey

Author: rafonseca

django-stubs/db/models/fields/related.pyi

@@ -29,7 +29,7 @@ def resolve_relation(scope_model: type[Model], relation: str | type[Model]) -> s
 # __set__ value type
 _ST = TypeVar("_ST")
 # __get__ return type
-_GT = TypeVar("_GT")
+_GT = TypeVar("_GT", default=_ST)
 
 class RelatedField(FieldCacheMixin, Field[_ST, _GT]):
     one_to_many: bool

tests/typecheck/models/test_related_fields.yml

@@ -142,3 +142,58 @@
 
         class Other(models.Model):
             field = models.ForeignKey(MyModel, related_name="others", on_delete=models.CASCADE)
+
+
+- case: test_related_fields_with_two_generic_parameters
+  main: |
+        from myapp.models import Address, School, Student
+        reveal_type(Student().school)  # N: Revealed type is "myapp.models.School"
+        reveal_type(Student().address)  # N: Revealed type is "myapp.models.Address"
+        s = Student()
+        s.school = School()
+        s.address = Address()
+  installed_apps:
+    - myapp
+  files:
+    - path: myapp/__init__.py
+    - path: myapp/models.py
+      content: |
+        from django.db import models
+
+        class School(models.Model):
+            pass
+
+        class Address(models.Model):
+            pass
+
+        class Student(models.Model):
+            school = models.ForeignKey["School","School"](to="School", on_delete=models.CASCADE)
+            address = models.OneToOneField["Address","Address"](to="Address", on_delete=models.CASCADE)
+
+
+- case: test_related_fields_with_one_generic_parameter
+  expect_fail: True
+  main: |
+        from myapp.models import Address, School, Student
+        reveal_type(Student().school)  # N: Revealed type is "myapp.models.School"
+        reveal_type(Student().address)  # N: Revealed type is "myapp.models.Address"
+        s = Student()
+        s.school = School()
+        s.address = Address()
+  installed_apps:
+    - myapp
+  files:
+    - path: myapp/__init__.py
+    - path: myapp/models.py
+      content: |
+        from django.db import models
+
+        class School(models.Model):
+            pass
+
+        class Address(models.Model):
+            pass
+
+        class Student(models.Model):
+            school = models.ForeignKey["School"](to="School", on_delete=models.CASCADE)
+            address = models.OneToOneField["Address"](to="Address", on_delete=models.CASCADE)