Fix issue when merging tags when the item has both the old and new tag

taggit/admin.py

@@ -27,7 +27,7 @@ def get_urls(self):
             path(
                 "merge-tags/",
                 self.admin_site.admin_view(self.merge_tags_view),
-                name="merge_tags",
+                name="taggit_tag_merge_tags",
             ),
         ]
         return custom_urls + urls
@@ -58,9 +58,18 @@ def merge_tags_view(self, request):
                         tag = Tag.objects.get(id=tag_id)
                         tagged_items = TaggedItem.objects.filter(tag=tag)
                         for tagged_item in tagged_items:
-                            tagged_item.tag = new_tag
-                            TaggedItem.objects.filter(tag=tag).update(tag=new_tag)
-                        # tag.delete()  #this will delete the selected tags after merge...leaving out for now
+                            if TaggedItem.objects.filter(
+                                tag=new_tag,
+                                content_type=tagged_item.content_type,
+                                object_id=tagged_item.object_id,
+                            ).exists():
+                                # we have the new tag as well, so we can just
+                                # remove the tag association
+                                tagged_item.delete()
+                            else:
+                                # point this taggedItem to the new one
+                                tagged_item.tag = new_tag
+                                tagged_item.save()
 
                 self.message_user(request, "Tags have been merged", level="success")
                 # clear the selected_tag_ids from session after merge is complete

taggit/templates/admin/taggit/merge_tags_form.html

@@ -6,7 +6,7 @@
         <form
           id="merge-tags-form"
           method="post"
-          action="{% url 'admin:merge_tags' %}"
+          action="{% url 'admin:taggit_tag_merge_tags' %}"
         >
           {% csrf_token %} {% for field in form %}
           <div>

tests/test_admin.py

@@ -1,6 +1,7 @@
 from django.contrib.auth.models import User
 from django.test import TestCase
 from django.urls import reverse
+from taggit.models import Tag
 
 from .models import Food
 
@@ -10,6 +11,11 @@ def setUp(self):
         super().setUp()
         self.apple = Food.objects.create(name="apple")
         self.apple.tags.add("Red", "red")
+        self.pear = Food.objects.create(name="pear")
+        self.pear.tags.add("red", "RED")
+        self.peach = Food.objects.create(name="peach")
+        self.peach.tags.add("red", "Yellow")
+
         user = User.objects.create_superuser(
             username="admin", email="[email protected]", password="password"
         )
@@ -40,3 +46,33 @@ def test_get_change(self):
             reverse("admin:tests_food_change", args=(self.apple.pk,))
         )
         self.assertEqual(response.status_code, 200)
+
+    def test_tag_merging(self):
+        response = self.client.get(reverse("admin:taggit_tag_changelist"))
+
+        # merging red and RED into Red
+        pks_to_select = [Tag.objects.get(name="red").pk, Tag.objects.get(name="RED").pk]
+        response = self.client.post(
+            reverse("admin:taggit_tag_changelist"),
+            data={"action": "render_tag_form", "_selected_action": pks_to_select},
+        )
+        # we're redirecting
+        self.assertEqual(response.status_code, 302)
+        # make sure what we expected got into the session keys
+        assert "selected_tag_ids" in self.client.session.keys()
+        self.assertEqual(
+            self.client.session["selected_tag_ids"], ",".join(map(str, pks_to_select))
+        )
+
+        # let's do the actual merge operation
+        response = self.client.post(
+            reverse("admin:taggit_tag_merge_tags"), {"new_tag_name": "Red"}
+        )
+        self.assertEqual(response.status_code, 302)
+
+        # time to check the result of the merges
+        self.assertSetEqual({tag.name for tag in self.apple.tags.all()}, {"Red"})
+        self.assertSetEqual({tag.name for tag in self.pear.tags.all()}, {"Red"})
+        self.assertSetEqual(
+            {tag.name for tag in self.peach.tags.all()}, {"Yellow", "Red"}
+        )