id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
19525	Regression: FileField calls validate during form validation; breaks auto_now_add date fields	Russell Keith-Magee	Aymeric Augustin	"As of dcd43831 (fixing #9893), a FileField will call `generate_filename()` as part of the validation step for a FileField on a form.  This was then updated in  05d333ba to address #18515. 

Unfortunately, this means that the filename function provided as an argument to upload_to can no longer reference any field with a pre-save behavior. 

The common use case for this is to organize files on disk according to upload date. For example:

{{{
def user_filename(instance, filename):
    return os.path.join('user_files', instance.uploaded_timestamp.strftime('%Y-%m-%d'), filename)

class UserFile(models.Model):
    uploaded_timestamp = models.DateTimeField(auto_now_add=True)
    data = models.FileField(upload_to=user_filename)
}}}

Under Django 1.5, attempting to call is_valid() on a Modelform for this model will raise a ""'NoneType' object has no attribute 'strftime'"" exception, because instance.uploaded_timestamp hasn't been instantiated yet. This is despite the fact that the uploaded data has been provided, the generated filename would be valid, and the upload timestamp can be computed.

In Django 1.4 and earlier, this works because no validation was performed for FileFields filenames; the uploaded_timestamp was evaluated as part of the model pre-save, and the persistence of the file to disk occurred after the model was saved.

To my reading, [https://docs.djangoproject.com/en/1.4/ref/models/fields/#django.db.models.FileField.upload_to the documentation is ambiguous] on whether this is  expected behavior or not. It says that the model may not be saved to the database yet, but points at AutoField as the cause for problems. However, it also explicitly talks about using strftime as part of file paths. A file datetimes of 'now' would seem to be an obvious usage of this feature.
"	Bug	closed	File uploads/storage	1.5-beta-1	Release blocker	fixed			Accepted	0	0	0	0	0	0