Fix similar_objects() in multi inheritance contexts (KeyError) (#712)

* Rename Django's dev branch to main.

More information: https://groups.google.com/g/django-developers/c/tctDuKUGosc/
Refs: django/django#14048

* Add tests demonstrating similar_objects exceptions due to multi inheritance.

* Fix similar_objects to resolve field_names for multi inheritance.

* Moved hand-crafted migrations to django-automated migration.

Co-authored-by: Jannis Leidel <jannis@leidel.info>

taggit/managers.py

@@ -387,8 +387,9 @@ def similar_objects(self):
                     % remote_field.field_name: [r["content_object"] for r in qs]
                 }
             )
+            actual_remote_field_name = f.target_field.get_attname()
             for obj in objs:
-                items[(getattr(obj, remote_field.field_name),)] = obj
+                items[(getattr(obj, actual_remote_field_name),)] = obj
         else:
             preload = {}
             for result in qs:

tests/migrations/0003_auto_20210310_0918.py

@@ -0,0 +1,93 @@
+# Generated by Django 3.1.7 on 2021-03-10 09:18
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+import taggit.managers
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("taggit", "0003_taggeditem_add_unique_index"),
+        ("contenttypes", "0002_remove_content_type_name"),
+        ("tests", "0002_auto_20200214_1129"),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name="BaseFood",
+            fields=[
+                (
+                    "id",
+                    models.AutoField(
+                        auto_created=True,
+                        primary_key=True,
+                        serialize=False,
+                        verbose_name="ID",
+                    ),
+                ),
+                ("name", models.CharField(max_length=50)),
+            ],
+        ),
+        migrations.CreateModel(
+            name="MultiInheritanceFood",
+            fields=[
+                (
+                    "basefood_ptr",
+                    models.OneToOneField(
+                        auto_created=True,
+                        on_delete=django.db.models.deletion.CASCADE,
+                        parent_link=True,
+                        primary_key=True,
+                        serialize=False,
+                        to="tests.basefood",
+                    ),
+                ),
+            ],
+            bases=("tests.basefood",),
+        ),
+        migrations.CreateModel(
+            name="MultiInheritanceLazyResolutionFoodTag",
+            fields=[
+                (
+                    "id",
+                    models.AutoField(
+                        auto_created=True,
+                        primary_key=True,
+                        serialize=False,
+                        verbose_name="ID",
+                    ),
+                ),
+                (
+                    "tag",
+                    models.ForeignKey(
+                        on_delete=django.db.models.deletion.CASCADE,
+                        related_name="tests_multiinheritancelazyresolutionfoodtag_items",
+                        to="taggit.tag",
+                    ),
+                ),
+                (
+                    "content_object",
+                    models.ForeignKey(
+                        on_delete=django.db.models.deletion.CASCADE,
+                        related_name="tagged_items",
+                        to="tests.multiinheritancefood",
+                    ),
+                ),
+            ],
+            options={
+                "unique_together": {("content_object", "tag")},
+            },
+        ),
+        migrations.AddField(
+            model_name="multiinheritancefood",
+            name="tags",
+            field=taggit.managers.TaggableManager(
+                help_text="A comma-separated list of tags.",
+                through="tests.MultiInheritanceLazyResolutionFoodTag",
+                to="taggit.Tag",
+                verbose_name="Tags",
+            ),
+        ),
+    ]

tests/models.py

@@ -57,6 +57,29 @@ def __str__(self):
         return self.name
 
 
+class BaseFood(models.Model):
+    name = models.CharField(max_length=50)
+
+    def __str__(self):
+        return self.name
+
+
+class MultiInheritanceLazyResolutionFoodTag(TaggedItemBase):
+    content_object = models.ForeignKey(
+        "MultiInheritanceFood", related_name="tagged_items", on_delete=models.CASCADE
+    )
+
+    class Meta:
+        unique_together = [["content_object", "tag"]]
+
+
+class MultiInheritanceFood(BaseFood):
+    tags = TaggableManager(through=MultiInheritanceLazyResolutionFoodTag)
+
+    def __str__(self):
+        return self.name
+
+
 class Pet(models.Model):
     name = models.CharField(max_length=50)
 

tests/tests.py

@@ -39,6 +39,7 @@
     Food,
     HousePet,
     Movie,
+    MultiInheritanceFood,
     Name,
     OfficialFood,
     OfficialHousePet,
@@ -164,6 +165,7 @@ class TagUUIDModelTestCase(TagModelTestCase):
 
 class TaggableManagerTestCase(BaseTaggingTestCase):
     food_model = Food
+    multi_inheritance_food_model = MultiInheritanceFood
     pet_model = Pet
     housepet_model = HousePet
     taggeditem_model = TaggedItem
@@ -606,6 +608,21 @@ def test_exclude(self):
             ordered=False,
         )
 
+    def test_multi_inheritance_similarity_by_tag(self):
+        """Test that pears are more similar to apples than watermelons using multi_inheritance"""
+        apple = self.multi_inheritance_food_model.objects.create(name="apple")
+        apple.tags.add("green", "juicy", "small", "sour")
+
+        pear = self.multi_inheritance_food_model.objects.create(name="pear")
+        pear.tags.add("green", "juicy", "small", "sweet")
+
+        watermelon = self.multi_inheritance_food_model.objects.create(name="watermelon")
+        watermelon.tags.add("green", "juicy", "large", "sweet")
+
+        similar_objs = apple.tags.similar_objects()
+        self.assertEqual(similar_objs, [pear, watermelon])
+        self.assertEqual([obj.similar_tags for obj in similar_objs], [3, 2])
+
     def test_similarity_by_tag(self):
         """Test that pears are more similar to apples than watermelons"""
         apple = self.food_model.objects.create(name="apple")