Add tests demonstrated Polymorphic through relationships in M2M admin fields

src/polymorphic/tests/admin.py

@@ -1,5 +1,5 @@
 from inspect import isclass
-from django.contrib.admin import register, ModelAdmin, site as admin_site
+from django.contrib.admin import register, ModelAdmin, TabularInline, site as admin_site
 from django.db.models.query import QuerySet
 from django.http import HttpRequest
 from polymorphic.admin import (
@@ -25,6 +25,15 @@
     M2MAdminTestChildA,
     M2MAdminTestChildB,
     M2MAdminTestChildC,
+    M2MThroughBase,
+    M2MThroughProject,
+    M2MThroughPerson,
+    M2MThroughMembership,
+    M2MThroughMembershipWithPerson,
+    M2MThroughMembershipWithSpecialPerson,
+    M2MThroughProjectWithTeam,
+    M2MThroughSpecialPerson,
+    DirectM2MContainer,
 )
 
 
@@ -104,3 +113,87 @@ class M2MAdminTestChildB(PolymorphicChildModelAdmin):
 @register(M2MAdminTestChildC)
 class M2MAdminTestChildC(PolymorphicChildModelAdmin):
     raw_id_fields = ("child_as",)
+
+
+# Issue #182: M2M field in model admin
+# Register models to test M2M field to polymorphic model
+@register(M2MThroughBase)
+class M2MThroughBaseAdmin(PolymorphicParentModelAdmin):
+    """Base admin for polymorphic M2M test models."""
+
+    child_models = (
+        M2MThroughProject,
+        M2MThroughPerson,
+        M2MThroughProjectWithTeam,
+        M2MThroughSpecialPerson,
+    )
+
+
+@register(M2MThroughProject)
+class M2MThroughProjectAdmin(PolymorphicChildModelAdmin):
+    """Admin for M2MThroughProject polymorphic child."""
+
+    pass
+
+
+@register(M2MThroughPerson)
+class M2MThroughPersonAdmin(PolymorphicChildModelAdmin):
+    """Admin for M2MThroughPerson polymorphic child."""
+
+    pass
+
+
+@register(M2MThroughSpecialPerson)
+class M2MThroughSpecialPersonAdmin(PolymorphicChildModelAdmin):
+    """Admin for M2MThroughSpecialPerson polymorphic child."""
+
+    pass
+
+
+@register(DirectM2MContainer)
+class DirectM2MContainerAdmin(ModelAdmin):
+    """
+    Test case for Issue #182: M2M field in model admin.
+    DirectM2MContainer has a direct M2M field to polymorphic M2MThroughBase model.
+    This should work without AttributeError: 'int' object has no attribute 'pk'.
+    """
+
+    filter_horizontal = ("items",)
+
+
+# Issue #375: Admin with M2M through table on polymorphic model
+class M2MThroughMembershipInline(StackedPolymorphicInline):
+    """
+    Polymorphic inline for Issue #375: M2M through table with polymorphic membership types.
+    This tests creating different membership types inline based on person type.
+    """
+
+    model = M2MThroughMembership
+    extra = 1
+
+    class MembershipWithPersonChild(StackedPolymorphicInline.Child):
+        """Inline for regular Person membership."""
+
+        model = M2MThroughMembershipWithPerson
+
+    class MembershipWithSpecialPersonChild(StackedPolymorphicInline.Child):
+        """Inline for SpecialPerson membership with special notes."""
+
+        model = M2MThroughMembershipWithSpecialPerson
+
+    child_inlines = (
+        MembershipWithPersonChild,
+        MembershipWithSpecialPersonChild,
+    )
+
+
+@register(M2MThroughProjectWithTeam)
+class M2MThroughProjectWithTeamAdmin(PolymorphicInlineSupportMixin, PolymorphicChildModelAdmin):
+    """
+    Test case for Issue #375: Admin with M2M through table on polymorphic model.
+    M2MThroughProjectWithTeam (polymorphic) has M2M to M2MThroughPerson (polymorphic)
+    with custom through model M2MThroughMembership (now polymorphic).
+    Uses polymorphic inlines to support different membership types.
+    """
+
+    inlines = (M2MThroughMembershipInline,)

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

@@ -1,4 +1,4 @@
-# Generated by Django 4.2 on 2026-01-07 11:43
+# Generated by Django 4.2 on 2026-01-07 13:29
 
 from decimal import Decimal
 from django.conf import settings
@@ -12,8 +12,8 @@ class Migration(migrations.Migration):
     initial = True
 
     dependencies = [
-        ('contenttypes', '0002_remove_content_type_name'),
         migrations.swappable_dependency(settings.AUTH_USER_MODEL),
+        ('contenttypes', '0002_remove_content_type_name'),
     ]
 
     operations = [

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

@@ -1,4 +1,4 @@
-# Generated by Django 4.2 on 2026-01-07 11:43
+# Generated by Django 4.2 on 2026-01-07 13:29
 
 from django.conf import settings
 from django.db import migrations, models
@@ -205,6 +205,31 @@ class Migration(migrations.Migration):
                 'base_manager_name': 'objects',
             },
         ),
+        migrations.CreateModel(
+            name='M2MThroughBase',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('name', models.CharField(max_length=50)),
+                ('polymorphic_ctype', models.ForeignKey(editable=False, null=True, on_delete=django.db.models.deletion.CASCADE, related_name='polymorphic_%(app_label)s.%(class)s_set+', to='contenttypes.contenttype')),
+            ],
+            options={
+                'abstract': False,
+                'base_manager_name': 'objects',
+            },
+        ),
+        migrations.CreateModel(
+            name='M2MThroughMembership',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('role', models.CharField(max_length=50)),
+                ('joined_date', models.DateField(auto_now_add=True)),
+                ('polymorphic_ctype', models.ForeignKey(editable=False, null=True, on_delete=django.db.models.deletion.CASCADE, related_name='polymorphic_%(app_label)s.%(class)s_set+', to='contenttypes.contenttype')),
+            ],
+            options={
+                'abstract': False,
+                'base_manager_name': 'objects',
+            },
+        ),
         migrations.CreateModel(
             name='Model2A',
             fields=[
@@ -614,6 +639,53 @@ class Migration(migrations.Migration):
             },
             bases=('tests.m2madmintest',),
         ),
+        migrations.CreateModel(
+            name='M2MThroughMembershipWithPerson',
+            fields=[
+                ('m2mthroughmembership_ptr', models.OneToOneField(auto_created=True, on_delete=django.db.models.deletion.CASCADE, parent_link=True, primary_key=True, serialize=False, to='tests.m2mthroughmembership')),
+            ],
+            options={
+                'abstract': False,
+                'base_manager_name': 'objects',
+            },
+            bases=('tests.m2mthroughmembership',),
+        ),
+        migrations.CreateModel(
+            name='M2MThroughMembershipWithSpecialPerson',
+            fields=[
+                ('m2mthroughmembership_ptr', models.OneToOneField(auto_created=True, on_delete=django.db.models.deletion.CASCADE, parent_link=True, primary_key=True, serialize=False, to='tests.m2mthroughmembership')),
+                ('special_notes', models.TextField(blank=True, default='')),
+            ],
+            options={
+                'abstract': False,
+                'base_manager_name': 'objects',
+            },
+            bases=('tests.m2mthroughmembership',),
+        ),
+        migrations.CreateModel(
+            name='M2MThroughPerson',
+            fields=[
+                ('m2mthroughbase_ptr', models.OneToOneField(auto_created=True, on_delete=django.db.models.deletion.CASCADE, parent_link=True, primary_key=True, serialize=False, to='tests.m2mthroughbase')),
+                ('email', models.EmailField(blank=True, max_length=254)),
+            ],
+            options={
+                'abstract': False,
+                'base_manager_name': 'objects',
+            },
+            bases=('tests.m2mthroughbase',),
+        ),
+        migrations.CreateModel(
+            name='M2MThroughProject',
+            fields=[
+                ('m2mthroughbase_ptr', models.OneToOneField(auto_created=True, on_delete=django.db.models.deletion.CASCADE, parent_link=True, primary_key=True, serialize=False, to='tests.m2mthroughbase')),
+                ('description', models.TextField(blank=True)),
+            ],
+            options={
+                'abstract': False,
+                'base_manager_name': 'objects',
+            },
+            bases=('tests.m2mthroughbase',),
+        ),
         migrations.CreateModel(
             name='Middle',
             fields=[
@@ -1267,6 +1339,14 @@ class Migration(migrations.Migration):
             name='lake',
             field=models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to='tests.lakewiththrough'),
         ),
+        migrations.CreateModel(
+            name='DirectM2MContainer',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('name', models.CharField(max_length=50)),
+                ('items', models.ManyToManyField(blank=True, related_name='containers', to='tests.m2mthroughbase')),
+            ],
+        ),
         migrations.AddField(
             model_name='derivedmanagertest',
             name='related_test',
@@ -1464,6 +1544,18 @@ class Migration(migrations.Migration):
             },
             bases=('tests.m2madmintestchildb',),
         ),
+        migrations.CreateModel(
+            name='M2MThroughSpecialPerson',
+            fields=[
+                ('m2mthroughperson_ptr', models.OneToOneField(auto_created=True, on_delete=django.db.models.deletion.CASCADE, parent_link=True, primary_key=True, serialize=False, to='tests.m2mthroughperson')),
+                ('special_code', models.CharField(blank=True, max_length=20)),
+            ],
+            options={
+                'abstract': False,
+                'base_manager_name': 'objects',
+            },
+            bases=('tests.m2mthroughperson',),
+        ),
         migrations.CreateModel(
             name='Model2C',
             fields=[
@@ -1607,6 +1699,11 @@ class Migration(migrations.Migration):
                 ('user_profiles', models.ManyToManyField(related_name='user_teams', to='tests.userprofile')),
             ],
         ),
+        migrations.AddField(
+            model_name='m2mthroughmembership',
+            name='person',
+            field=models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to='tests.m2mthroughperson'),
+        ),
         migrations.AddField(
             model_name='m2madmintestchilda',
             name='child_bs',
@@ -1686,6 +1783,23 @@ class Migration(migrations.Migration):
             },
             bases=('tests.uuidartprojecta',),
         ),
+        migrations.CreateModel(
+            name='M2MThroughProjectWithTeam',
+            fields=[
+                ('m2mthroughproject_ptr', models.OneToOneField(auto_created=True, on_delete=django.db.models.deletion.CASCADE, parent_link=True, primary_key=True, serialize=False, to='tests.m2mthroughproject')),
+                ('team', models.ManyToManyField(blank=True, related_name='projects', through='tests.M2MThroughMembership', to='tests.m2mthroughperson')),
+            ],
+            options={
+                'abstract': False,
+                'base_manager_name': 'objects',
+            },
+            bases=('tests.m2mthroughproject',),
+        ),
+        migrations.AddField(
+            model_name='m2mthroughmembership',
+            name='project',
+            field=models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to='tests.m2mthroughprojectwithteam'),
+        ),
         migrations.CreateModel(
             name='UUIDArtProjectC',
             fields=[

src/polymorphic/tests/models.py

@@ -907,3 +907,84 @@ class M2MAdminTestChildB(M2MAdminTest):
 
 class M2MAdminTestChildC(M2MAdminTestChildB):
     pass
+
+
+# Models for testing Issue #182 and #375: M2M with through tables to/from polymorphic models
+class M2MThroughBase(PolymorphicModel):
+    """Base polymorphic model for M2M through table tests."""
+
+    name = models.CharField(max_length=50)
+
+    def __str__(self):
+        return self.name
+
+
+class M2MThroughPerson(M2MThroughBase):
+    """Polymorphic child representing a person who can be on teams."""
+
+    email = models.EmailField(blank=True)
+
+
+class M2MThroughSpecialPerson(M2MThroughPerson):
+    """Polymorphic child representing a special person."""
+
+    special_code = models.CharField(max_length=20, blank=True)
+
+
+class M2MThroughProject(M2MThroughBase):
+    """Polymorphic child representing a project."""
+
+    description = models.TextField(blank=True)
+
+
+class M2MThroughProjectWithTeam(M2MThroughProject):
+    """
+    Polymorphic child with M2M to Person through Membership.
+    Tests Issue #375: M2M with through table on polymorphic model.
+    """
+
+    pass
+
+
+class M2MThroughMembership(PolymorphicModel):
+    """Polymorphic through model for M2M relationship between ProjectWithTeam and Person."""
+
+    project = models.ForeignKey("M2MThroughProjectWithTeam", on_delete=models.CASCADE)
+    person = models.ForeignKey(M2MThroughPerson, on_delete=models.CASCADE)
+    role = models.CharField(max_length=50)
+    joined_date = models.DateField(auto_now_add=True)
+
+    def __str__(self):
+        return f"{self.person.name} - {self.role} on {self.project.name}"
+
+
+class M2MThroughMembershipWithPerson(M2MThroughMembership):
+    """Membership for regular Person instances."""
+
+    pass
+
+
+class M2MThroughMembershipWithSpecialPerson(M2MThroughMembership):
+    """Membership for SpecialPerson instances with additional tracking."""
+
+    special_notes = models.TextField(blank=True, default="")
+
+
+# Add the M2M field after the through model is defined
+M2MThroughProjectWithTeam.add_to_class(
+    "team",
+    models.ManyToManyField(
+        M2MThroughPerson, through=M2MThroughMembership, related_name="projects", blank=True
+    ),
+)
+
+
+# Additional models for Issue #182: Direct M2M to polymorphic model
+class DirectM2MContainer(models.Model):
+    """Non-polymorphic model with direct M2M to polymorphic model."""
+
+    name = models.CharField(max_length=50)
+    items = models.ManyToManyField(M2MThroughBase, related_name="containers", blank=True)
+
+    def __str__(self):
+        return self.name