Ticket #18515: 18515-1.diff

django/db/models/fields/files.py

@@ -242 +242 @@
         # (ie. upload_to='path/to/upload/dir'), the length of the generated
         # name equals the length of the uploaded name plus a constant. Thus
         # we can tell the user how much shorter the name should be (roughly).
-        length = len(self.generate_filename(model_instance, value.name))
+        if value and value._committed:
+            filename = value.name
+        else:
+            filename = self.generate_filename(model_instance, value.name)
+        length = len(filename)
         if self.max_length and length > self.max_length:
             error_values = {'extra': length - self.max_length}
             raise ValidationError(self.error_messages['max_length'] % error_values)

tests/modeltests/files/models.py

@@ -26 +26 @@
 
     normal = models.FileField(storage=temp_storage, upload_to='tests')
     custom = models.FileField(storage=temp_storage, upload_to=custom_upload_to)
-    random = models.FileField(storage=temp_storage, upload_to=random_upload_to)
+    random = models.FileField(storage=temp_storage, upload_to=random_upload_to, max_length=16)
     default = models.FileField(storage=temp_storage, upload_to='tests', default='tests/default.txt')

tests/modeltests/files/tests.py

@@ -102 +102 @@
         obj4.random.save("random_file", ContentFile(b"random content"))
         self.assertTrue(obj4.random.name.endswith("/random_file"))
 
+        # Ticket #18515: validation for an already saved file should not check
+        # against a regenerated file name (and potentially raise a ValidationError
+        # if max_length is exceeded)
+        obj4.full_clean()
+
         # Clean up the temporary files and dir.
         obj1.normal.delete()
         obj2.normal.delete()