Optimize Collector to fetch only required fields for delete

Avoids loading unnecessary or problematic data (e.g., invalid Unicode in text fields) during cascaded .delete(), improving performance and preventing decode errors.

Helps resolve UnicodeDecodeError seen in data purging (#21961).

django/db/models/deletion.py

@@ -232,9 +232,20 @@ class Collector:
         """
         Get a QuerySet of objects related to `objs` via the relation `related`.
         """
-        return related.related_model._base_manager.using(self.using).filter(
+        qs = related.related_model._base_manager.using(self.using).filter(
             **{"%s__in" % related.field.name: objs}
         )
+        # Fetch only the fields needed for deletion to avoid loading
+        # potentially problematic data (e.g., invalid Unicode in text fields):
+        # - Primary key (for deletion SQL and sorting)
+        # - Foreign key fields (for signals, parent cascade, and field updates)
+        model = related.related_model
+        fields = [model._meta.pk.name]
+        # Add all foreign key fields (including parent links)
+        for field in model._meta.concrete_fields:
+            if field.many_to_one and field.name != model._meta.pk.name:
+                fields.append(field.name)
+        return qs.only(*fields)
 
     def instances_with_model(self):
         for model, instances in self.data.items():