Handle non-JSON-safe fields in exclude_fields_in_copy

Fixes #11715

When copying a page's revision history, fields listed in exclude_fields_on_copy are replaced with the new value from the copied page instance (which has already had the exclude_fields_on_copy logic applied by this point, meaning that we'll get the model's default value instead). However, this does not take into account whether the value from the instance is JSON-serializable. This causes it to break when the field is a one-to-many or many-to-many relation, which returns the manager object (#11715), or a field that works with non-JSON-safe values such as StreamField.

Also, the old code was using the page model's exclude_fields_on_copy rather than the exclude_fields variable which also includes `default_exclude_fields_in_copy` and the passed-in `exclude_fields` argument - this meant that core fields such as `url_path` were not being replaced as expected.

CHANGELOG.txt

@@ -20,6 +20,7 @@ Changelog
  * Fix: Ensure `WAGTAILADMIN_LOGIN_URL` is respected when logging out of the admin (Antoine Rodriguez, Ramon de Jezus)
  * Fix: Fix behaviour of `ViewSet.inject_view_methods` with multiple methods (Gorlik)
  * Fix: Preserve query strings in URLs submitted to CloudFront for invalidation (Jigyasu Rajput)
+ * Fix: Handle non-JSON-safe fields in `exclude_fields_in_copy` (Matt Westcott)
  * Maintenance: Refactor `get_embed` to remove `finder` argument which was only used for mocking in unit tests (Jigyasu Rajput)
  * Maintenance: Simplify handling of `None` values in `TypedTableBlock` (Jigyasu Rajput)
  * Maintenance: Remove squash.io configuration (Sage Abdullah)

docs/releases/7.1.md

@@ -32,6 +32,7 @@ depth: 1
  * Ensure `WAGTAILADMIN_LOGIN_URL` is respected when logging out of the admin (Antoine Rodriguez, Ramon de Jezus)
  * Fix behaviour of `ViewSet.inject_view_methods` with multiple methods (Gorlik)
  * Preserve query strings in URLs submitted to CloudFront for invalidation (Jigyasu Rajput)
+ * Handle non-JSON-safe fields in `exclude_fields_in_copy` (Matt Westcott)
 
 ### Documentation
 

wagtail/actions/copy_page.py

@@ -181,6 +181,11 @@ class CopyPageAction:
 
         # Copy revisions
         if self.copy_revisions:
+            # Fetch data for the new page copy in the same serializable format that would be
+            # written to revisions. Any field in exclude_fields that is found in the revision data
+            # will be replaced with the corresponding field from here.
+            page_copy_data = page_copy.serializable_data()
+
             for revision in page.revisions.all():
                 use_as_latest_revision = revision.pk == page.latest_revision_id
                 revision.pk = None
@@ -221,13 +226,9 @@ class CopyPageAction:
                                 )
                             )
 
-                for exclude_field in specific_page.exclude_fields_in_copy:
-                    if exclude_field in revision_content and hasattr(
-                        page_copy, exclude_field
-                    ):
-                        revision_content[exclude_field] = getattr(
-                            page_copy, exclude_field, None
-                        )
+                for field_name in exclude_fields:
+                    if field_name in revision_content:
+                        revision_content[field_name] = page_copy_data.get(field_name)
 
                 revision.content = revision_content
 

wagtail/test/testapp/migrations/0053_pagewithexcludedcopyfield_special_stream_and_more.py

@@ -0,0 +1,57 @@
+# Generated by Django 5.2.1 on 2025-05-16 10:44
+
+import django.db.models.deletion
+import modelcluster.fields
+from django.db import migrations, models
+
+import wagtail.fields
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("tests", "0052_variousondeletemodel_protected_page_and_user"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="pagewithexcludedcopyfield",
+            name="special_stream",
+            field=wagtail.fields.StreamField(
+                [("item", 0)],
+                block_lookup={0: ("wagtail.blocks.CharBlock", (), {})},
+                default=[("item", "default item")],
+            ),
+        ),
+        migrations.CreateModel(
+            name="ExcludedCopyPageNote",
+            fields=[
+                (
+                    "id",
+                    models.AutoField(
+                        auto_created=True,
+                        primary_key=True,
+                        serialize=False,
+                        verbose_name="ID",
+                    ),
+                ),
+                (
+                    "sort_order",
+                    models.IntegerField(blank=True, editable=False, null=True),
+                ),
+                ("note", models.CharField(max_length=255)),
+                (
+                    "page",
+                    modelcluster.fields.ParentalKey(
+                        on_delete=django.db.models.deletion.CASCADE,
+                        related_name="special_notes",
+                        to="tests.pagewithexcludedcopyfield",
+                    ),
+                ),
+            ],
+            options={
+                "ordering": ["sort_order"],
+                "abstract": False,
+            },
+        ),
+    ]

wagtail/test/testapp/models.py

@@ -240,18 +240,34 @@ class CustomPreviewSizesPage(Page):
         return "desktop"
 
 
+class ExcludedCopyPageNote(Orderable):
+    page = ParentalKey(
+        "tests.PageWithExcludedCopyField",
+        related_name="special_notes",
+        on_delete=models.CASCADE,
+    )
+    note = models.CharField(max_length=255)
+
+    panels = [FieldPanel("note")]
+
+
 # Page with Excluded Fields when copied
 class PageWithExcludedCopyField(Page):
     content = models.TextField()
 
-    # Exclude this field from being copied
+    # Exclude these fields and the special_notes relation from being copied
     special_field = models.CharField(blank=True, max_length=255, default="Very Special")
-    exclude_fields_in_copy = ["special_field"]
+    special_stream = StreamField(
+        [("item", CharBlock())], default=[("item", "default item")]
+    )
+    exclude_fields_in_copy = ["special_field", "special_notes", "special_stream"]
 
     content_panels = [
         TitleFieldPanel("title", classname="title"),
         FieldPanel("special_field"),
         FieldPanel("content"),
+        FieldPanel("special_stream"),
+        InlinePanel("special_notes", label="Special notes"),
     ]
 
 

wagtail/tests/test_page_model.py

@@ -1,4 +1,5 @@
 import datetime
+import json
 import unittest
 from unittest.mock import Mock
 
@@ -49,6 +50,7 @@ from wagtail.test.testapp.models import (
     EventIndex,
     EventPage,
     EventPageSpeaker,
+    ExcludedCopyPageNote,
     GenericSnippetPage,
     ManyToManyBlogPage,
     MTIBasePage,
@@ -1994,24 +1996,34 @@ class TestCopyPage(TestCase):
 
     def test_copy_page_with_additional_excluded_fields(self):
         homepage = Page.objects.get(url_path="/home/")
-        page = homepage.add_child(
-            instance=PageWithExcludedCopyField(
-                title="Discovery",
-                slug="disco",
-                content="NCC-1031",
-                special_field="Context is for Kings",
-            )
+        page = PageWithExcludedCopyField(
+            title="Discovery",
+            slug="disco",
+            content="NCC-1031",
+            special_field="Context is for Kings",
+            special_stream=[("item", "non-default item")],
         )
+        page.special_notes = [ExcludedCopyPageNote(note="Some note")]
+        homepage.add_child(instance=page)
         page.save_revision()
         new_page = page.copy(to=homepage, update_attrs={"slug": "disco-2"})
-        exclude_field = new_page.latest_revision.content["special_field"]
+        revision_content = new_page.latest_revision.content
 
         self.assertEqual(page.title, new_page.title)
         self.assertNotEqual(page.id, new_page.id)
         self.assertNotEqual(page.path, new_page.path)
-        # special_field is in the list to be excluded
-        self.assertNotEqual(page.special_field, new_page.special_field)
-        self.assertEqual(new_page.special_field, exclude_field)
+
+        # special_field and special_stream are in the list to be excluded,
+        # and should revert to the default
+        self.assertEqual(new_page.special_field, "Very Special")
+        self.assertEqual(revision_content["special_field"], "Very Special")
+        self.assertEqual(new_page.special_stream[0].value, "default item")
+        stream_data = json.loads(revision_content["special_stream"])
+        self.assertEqual(stream_data[0]["value"], "default item")
+
+        # The special_notes relation should be cleared on the new page
+        self.assertEqual(new_page.special_notes.count(), 0)
+        self.assertEqual(revision_content["special_notes"], [])
 
     def test_page_with_generic_relation(self):
         """Test that a page with a GenericRelation will have that relation ignored when