use ignore_conflicts when inserting references

don't pass ignore_conflicts if backend is mssql

check for feature not DB engine

CHANGELOG.txt

@@ -55,6 +55,7 @@ Changelog
  * Fix: Prevent crash on snippet inspect view when displaying a null foreign key to an image (Sage Abdullah)
  * Fix: Ensure that pages in moderation show as "Live + In Moderation" in the page explorer rather than "Live + Draft" (Sage Abdullah)
  * Fix: Prevent error when updating reference index for objects with a lazy ParentalKey-related object (Chris Shaw)
+ * Fix: Ignore conflicts when inserting reference index entries to prevent race conditions causing uniqueness errors (Chris Shaw)
  * Docs: Document `WAGTAILADMIN_BASE_URL` on "Integrating Wagtail into a Django project" page (Shreshth Srivastava)
  * Docs: Replace incorrect screenshot for authors listing on tutorial (Shreshth Srivastava)
  * Docs: Add documentation for building non-model-based choosers using the _queryish_ library (Matt Westcott)

docs/releases/5.2.md

@@ -71,6 +71,7 @@ depth: 1
  * Prevent crash on snippet inspect view when displaying a null foreign key to an image (Sage Abdullah)
  * Ensure that pages in moderation show as "Live + In Moderation" in the page explorer rather than "Live + Draft" (Sage Abdullah)
  * Prevent error when updating reference index for objects with a lazy ParentalKey-related object (Chris Shaw)
+ * Ignore conflicts when inserting reference index entries to prevent race conditions causing uniqueness errors (Chris Shaw)
 
 ### Documentation
 

wagtail/models/reference_index.py

@@ -2,7 +2,7 @@ import uuid
 
 from django.contrib.contenttypes.fields import GenericForeignKey, GenericRel
 from django.contrib.contenttypes.models import ContentType
-from django.db import models
+from django.db import connection, models
 from django.utils.functional import cached_property
 from django.utils.text import capfirst
 from django.utils.translation import gettext_lazy as _
@@ -456,6 +456,11 @@ class ReferenceIndex(models.Model):
         # Construct the set of reference records that have been found on the object but are not
         # already present in the database
         new_references = references - set(existing_references.keys())
+
+        bulk_create_kwargs = {}
+        if connection.features.supports_ignore_conflicts:
+            bulk_create_kwargs["ignore_conflicts"] = True
+
         # Create database records for those reference records
         cls.objects.bulk_create(
             [
@@ -470,7 +475,8 @@ class ReferenceIndex(models.Model):
                     content_path_hash=cls._get_content_path_hash(content_path),
                 )
                 for to_content_type_id, to_object_id, model_path, content_path in new_references
-            ]
+            ],
+            **bulk_create_kwargs,
         )
 
         # Delete removed references