Fixed #35139 -- Prevented file read after ImageField is saved to storage.

django/db/models/fields/files.py

@@ -90,10 +90,13 @@ class FieldFile(File, AltersData):
     # to further manipulate the underlying file, as well as update the
     # associated model instance.
 
+    def _set_instance_attribute(self, name, content):
+        setattr(self.instance, self.field.attname, name)
+
     def save(self, name, content, save=True):
         name = self.field.generate_filename(self.instance, name)
         self.name = self.storage.save(name, content, max_length=self.field.max_length)
-        setattr(self.instance, self.field.attname, self.name)
+        self._set_instance_attribute(self.name, content)
         self._committed = True
 
         # Save the object because it has changed, unless save is False
@@ -391,6 +394,12 @@ class ImageFileDescriptor(FileDescriptor):
 
 
 class ImageFieldFile(ImageFile, FieldFile):
+    def _set_instance_attribute(self, name, content):
+        setattr(self.instance, self.field.attname, content)
+        # Update the name in case generate_filename() or storage.save() changed
+        # it, but bypass the descriptor to avoid re-reading the file.
+        self.instance.__dict__[self.field.attname] = self.name
+
     def delete(self, save=True):
         # Clear the image dimensions cache
         if hasattr(self, "_dimensions_cache"):

docs/releases/5.1.txt

@@ -437,6 +437,11 @@ Miscellaneous
   :class:`~django.core.exceptions.FieldError` when saving a file without a
   ``name``.
 
+* ``ImageField.update_dimension_fields(force=True)`` is no longer called after
+  saving the image to storage. If your storage backend resizes images, the
+  ``width_field`` and ``height_field`` will not match the width and height of
+  the image.
+
 .. _deprecated-features-5.1:
 
 Features deprecated in 5.1

tests/model_fields/models.py

@@ -13,6 +13,8 @@ from django.db.models.functions import Lower
 from django.utils.functional import SimpleLazyObject
 from django.utils.translation import gettext_lazy as _
 
+from .storage import NoReadFileSystemStorage
+
 try:
     from PIL import Image
 except ImportError:
@@ -373,6 +375,21 @@ if Image:
             width_field="headshot_width",
         )
 
+    class PersonNoReadImage(models.Model):
+        """
+        Model that defines an ImageField with a storage backend that does not
+        support reading.
+        """
+
+        mugshot = models.ImageField(
+            upload_to="tests",
+            storage=NoReadFileSystemStorage(),
+            width_field="mugshot_width",
+            height_field="mugshot_height",
+        )
+        mugshot_width = models.IntegerField()
+        mugshot_height = models.IntegerField()
+
 
 class CustomJSONDecoder(json.JSONDecoder):
     def __init__(self, object_hook=None, *args, **kwargs):

tests/model_fields/storage.py

@@ -0,0 +1,6 @@
+from django.core.files.storage.filesystem import FileSystemStorage
+
+
+class NoReadFileSystemStorage(FileSystemStorage):
+    def open(self, *args, **kwargs):
+        raise AssertionError("This storage class does not support reading.")

tests/model_fields/test_imagefield.py

@@ -18,6 +18,7 @@ if Image:
     from .models import (
         Person,
         PersonDimensionsFirst,
+        PersonNoReadImage,
         PersonTwoImages,
         PersonWithHeight,
         PersonWithHeightAndWidth,
@@ -30,7 +31,7 @@ else:
         pass
 
     PersonWithHeight = PersonWithHeightAndWidth = PersonDimensionsFirst = Person
-    PersonTwoImages = Person
+    PersonTwoImages = PersonNoReadImage = Person
 
 
 class ImageFieldTestMixin(SerializeMixin):
@@ -469,3 +470,28 @@ class TwoImageFieldTests(ImageFieldTestMixin, TestCase):
         # Dimensions were recalculated, and hence file should have opened.
         self.assertIs(p.mugshot.was_opened, True)
         self.assertIs(p.headshot.was_opened, True)
+
+
+@skipIf(Image is None, "Pillow is required to test ImageField")
+class NoReadTests(ImageFieldTestMixin, TestCase):
+    def test_width_height_correct_name_mangling_correct(self):
+        instance1 = PersonNoReadImage()
+
+        instance1.mugshot.save("mug", self.file1)
+
+        self.assertEqual(instance1.mugshot_width, 4)
+        self.assertEqual(instance1.mugshot_height, 8)
+
+        instance1.save()
+
+        self.assertEqual(instance1.mugshot_width, 4)
+        self.assertEqual(instance1.mugshot_height, 8)
+
+        instance2 = PersonNoReadImage()
+        instance2.mugshot.save("mug", self.file1)
+        instance2.save()
+
+        self.assertNotEqual(instance1.mugshot.name, instance2.mugshot.name)
+
+        self.assertEqual(instance1.mugshot_width, instance2.mugshot_width)
+        self.assertEqual(instance1.mugshot_height, instance2.mugshot_height)