[2.0.x] Fixed #28462 -- Decreased memory usage with ModelAdmin.list_editable.

Regression in 917cc288a38f3c114a5440f0749b7e5e1086eb36.

Backport of b18650a2634890aa758abae2f33875daa13a9ba3 from master

1 files changed, 24 insertions, 1 deletions

diff --git a/django/contrib/admin/options.py b/django/contrib/admin/options.py
index 1eee19fea4..8d8f263db1 100644
--- a/django/contrib/admin/options.py
+++ b/django/contrib/admin/options.py
@@ -1,6 +1,7 @@
 import copy
 import json
 import operator
+import re
 from collections import OrderedDict
 from functools import partial, reduce, update_wrapper
 from urllib.parse import quote as urlquote
@@ -1555,6 +1556,27 @@ class ModelAdmin(BaseModelAdmin):
     def change_view(self, request, object_id, form_url='', extra_context=None):
         return self.changeform_view(request, object_id, form_url, extra_context)
 
+    def _get_edited_object_pks(self, request, prefix):
+        """Return POST data values of list_editable primary keys."""
+        pk_pattern = re.compile('{}-\d+-{}$'.format(prefix, self.model._meta.pk.name))
+        return [value for key, value in request.POST.items() if pk_pattern.match(key)]
+
+    def _get_list_editable_queryset(self, request, prefix):
+        """
+        Based on POST data, return a queryset of the objects that were edited
+        via list_editable.
+        """
+        object_pks = self._get_edited_object_pks(request, prefix)
+        queryset = self.get_queryset(request)
+        validate = queryset.model._meta.pk.to_python
+        try:
+            for pk in object_pks:
+                validate(pk)
+        except ValidationError:
+            # Disable the optimization if the POST data was tampered with.
+            return queryset
+        return queryset.filter(pk__in=object_pks)
+
     @csrf_protect_m
     def changelist_view(self, request, extra_context=None):
         """
@@ -1629,7 +1651,8 @@ class ModelAdmin(BaseModelAdmin):
         # Handle POSTed bulk-edit data.
         if request.method == 'POST' and cl.list_editable and '_save' in request.POST:
             FormSet = self.get_changelist_formset(request)
-            formset = cl.formset = FormSet(request.POST, request.FILES, queryset=self.get_queryset(request))
+            modified_objects = self._get_list_editable_queryset(request, FormSet.get_default_prefix())
+            formset = cl.formset = FormSet(request.POST, request.FILES, queryset=modified_objects)
             if formset.is_valid():
                 changecount = 0
                 for form in formset.forms: