Fix: Admin Bugs

src/polymorphic/admin/parentadmin.py

@@ -12,7 +12,6 @@
 from django.template.response import TemplateResponse
 from django.urls import URLResolver
 from django.utils.encoding import force_str
-from django.utils.http import urlencode
 from django.utils.safestring import mark_safe
 from django.utils.translation import gettext_lazy as _
 
@@ -199,9 +198,11 @@ def add_view(self, request, form_url="", extra_context=None):
         else:
             real_admin = self._get_real_admin_by_ct(ct_id)
             # rebuild form_url, otherwise libraries below will override it.
+            # Preserve popup-related parameters to ensure popup functionality works
+            # correctly even after validation errors (issue #612)
             form_url = add_preserved_filters(
                 {
-                    "preserved_filters": urlencode({"ct_id": ct_id}),
+                    "preserved_filters": request.GET.urlencode(),
                     "opts": self.model._meta,
                 },
                 form_url,

src/polymorphic/tests/admin.py

@@ -20,6 +20,7 @@
     InlineModelB,
     InlineParent,
     NoChildren,
+    ModelWithPolyFK,
 )
 
 
@@ -73,3 +74,8 @@ class InlineParentAdmin(PolymorphicInlineSupportMixin, ModelAdmin):
 @register(NoChildren)
 class NoChildrenAdmin(PolymorphicParentModelAdmin):
     child_models = (NoChildren,)
+
+
+@register(ModelWithPolyFK)
+class ModelWithPolyFKAdmin(ModelAdmin):
+    fields = ["name", "poly_fk"]

src/polymorphic/tests/deletion/migrations/0001_initial.py

@@ -1,4 +1,4 @@
-# Generated by Django 4.2 on 2026-01-06 17:46
+# Generated by Django 4.2 on 2026-01-06 23:40
 
 from decimal import Decimal
 from django.conf import settings
@@ -12,8 +12,8 @@ class Migration(migrations.Migration):
     initial = True
 
     dependencies = [
-        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
         ('contenttypes', '0002_remove_content_type_name'),
+        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
     ]
 
     operations = [

src/polymorphic/tests/migrations/0001_initial.py

@@ -1,4 +1,4 @@
-# Generated by Django 4.2 on 2026-01-06 17:46
+# Generated by Django 4.2 on 2026-01-06 23:40
 
 from django.conf import settings
 from django.db import migrations, models
@@ -14,8 +14,8 @@ class Migration(migrations.Migration):
     initial = True
 
     dependencies = [
-        ('contenttypes', '0002_remove_content_type_name'),
         ('auth', '0012_alter_user_first_name_max_length'),
+        ('contenttypes', '0002_remove_content_type_name'),
     ]
 
     operations = [
@@ -1075,6 +1075,14 @@ class Migration(migrations.Migration):
                 'base_manager_name': 'objects',
             },
         ),
+        migrations.CreateModel(
+            name='ModelWithPolyFK',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('name', models.CharField(max_length=100)),
+                ('poly_fk', models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.CASCADE, to='tests.model2a')),
+            ],
+        ),
         migrations.CreateModel(
             name='ModelUnderRelParent',
             fields=[
@@ -1558,6 +1566,7 @@ class Migration(migrations.Migration):
             fields=[
                 ('inlinemodela_ptr', models.OneToOneField(auto_created=True, on_delete=django.db.models.deletion.CASCADE, parent_link=True, primary_key=True, serialize=False, to='tests.inlinemodela')),
                 ('field2', models.CharField(max_length=30)),
+                ('file_upload', models.FileField(blank=True, default=None, null=True, upload_to='test_uploads/')),
                 ('plain_a', models.ForeignKey(blank=True, default=None, null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='inline_bs', to='tests.plaina')),
             ],
             options={

src/polymorphic/tests/models.py

@@ -493,6 +493,9 @@ class InlineModelB(InlineModelA):
         related_name="inline_bs",
     )
 
+    # File field for testing multipart encoding in polymorphic inlines (issue #380)
+    file_upload = models.FileField(upload_to="test_uploads/", null=True, blank=True, default=None)
+
 
 class AbstractProject(PolymorphicModel):
     topic = models.CharField(max_length=30)
@@ -730,6 +733,13 @@ class NoChildren(PolymorphicModel):
     field1 = models.CharField(max_length=12)
 
 
+class ModelWithPolyFK(models.Model):
+    """Model with FK to polymorphic model for popup testing."""
+
+    name = models.CharField(max_length=100)
+    poly_fk = models.ForeignKey(Model2A, on_delete=models.CASCADE, null=True, blank=True)
+
+
 class NormalBase(models.Model):
     nb_field = models.IntegerField()