Fixed #18515 -- Conditionally regenerated filename in FileField validation

When a FileField value has been saved, a new validation should not
regenerate a new filename when checking the length. Refs #9893.

1 files changed, 5 insertions, 1 deletions

diff --git a/django/db/models/fields/files.py b/django/db/models/fields/files.py
index e0c095974d..b0dce381a6 100644
--- a/django/db/models/fields/files.py
+++ b/django/db/models/fields/files.py
@@ -242,7 +242,11 @@ class FileField(Field):
         # (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)