Fixed #27852 -- Fixed object deletion to show all protected related o…

…bjects rather than just the first one.

django/db/models/deletion.py

@@ -265,6 +265,7 @@ def collect(self, objs, source=None, nullable=False, collect_related=True,
         if keep_parents:
             parents = set(model._meta.get_parent_list())
         model_fast_deletes = defaultdict(list)
+        protected_objects = {'keys': [], 'sub_objs': []}
         for related in get_candidate_relations_to_delete(model._meta):
             # Preserve parent reverse relationships if keep_parents=True.
             if keep_parents and related.model in parents:
@@ -292,7 +293,22 @@ def collect(self, objs, source=None, nullable=False, collect_related=True,
                     ))
                     sub_objs = sub_objs.only(*tuple(referenced_fields))
                 if sub_objs:
-                    field.remote_field.on_delete(self, field, sub_objs, self.using)
+                    try:
+                        field.remote_field.on_delete(self, field, sub_objs, self.using)
+                    except ProtectedError:
+                        protected_objects['sub_objs'] += sub_objs
+                        protected_objects['keys'].append("'%s.%s'" % (sub_objs[0].__class__.__name__, field.name))
+
+        if protected_objects['keys']:
+            raise ProtectedError(
+                "Cannot delete some instances of model '%s' because they are "
+                "referenced through protected foreign keys: %s." % (
+                    field.remote_field.model.__name__,
+                    ', '.join(protected_objects['keys'])
+                ),
+                protected_objects['sub_objs'],
+            )
+
         for related_model, related_fields in model_fast_deletes.items():
             batches = self.get_del_batches(new_objs, related_fields)
             for batch in batches:

tests/delete/models.py

@@ -68,6 +68,10 @@ class A(models.Model):
     o2o_setnull = models.ForeignKey(R, models.SET_NULL, null=True, related_name="o2o_nullable_set")
 
 
+class B(models.Model):
+    protect = models.ForeignKey(R, models.PROTECT)
+
+
 def create_a(name):
     a = A(name=name)
     for name in ('auto', 'auto_nullable', 'setvalue', 'setnull', 'setdefault',

tests/delete/tests.py

@@ -6,7 +6,7 @@
 from django.test import TestCase, skipIfDBFeature, skipUnlessDBFeature
 
 from .models import (
-    B1, B2, MR, A, Avatar, Base, Child, DeleteBottom, DeleteTop, GenericB1,
+    B1, B2, MR, A, Avatar, B, Base, Child, DeleteBottom, DeleteTop, GenericB1,
     GenericB2, GenericDeleteBottom, HiddenUser, HiddenUserProfile, M, M2MFrom,
     M2MTo, MRNull, Origin, P, Parent, R, RChild, RChildChild, Referrer, S, T,
     User, create_a, get_default_r,
@@ -72,11 +72,21 @@ def test_protect(self):
         a = create_a('protect')
         msg = (
             "Cannot delete some instances of model 'R' because they are "
-            "referenced through a protected foreign key: 'A.protect'"
+            "referenced through protected foreign keys: 'A.protect'"
         )
         with self.assertRaisesMessage(IntegrityError, msg):
             a.protect.delete()
 
+    def test_protect_multiple(self):
+        a = create_a('protect')
+        B.objects.create(protect=a.protect)
+        with self.assertRaisesMessage(
+            IntegrityError,
+            "Cannot delete some instances of model 'R' because they are "
+            "referenced through protected foreign keys: 'A.protect', 'B.protect'"
+        ):
+            a.protect.delete()
+
     def test_do_nothing(self):
         # Testing DO_NOTHING is a bit harder: It would raise IntegrityError for a normal model,
         # so we connect to pre_delete and set the fk to a known value.