Documents _post_clean() does not handle None to EMPTY_VALUES conversion gracefully

[foxx]

If the DocumentForm has an optional StringField with no data value specified for it on the form instance, it will fail with;

StringField only accepts string values

This is because on documents.py#L439, a call is being made to validate() on the model field which in raises an exception.

Mongoengine handles this in save() by simply removing the field during to_mongo() as seen in mongoengine:document.py#L248.

Here's a few ideas on how it could be fixed;

• Prevent .validate() from being called on fields which are not specified in data
• Ignore any validation errors if the field is optional and the value is None
• Convert None to the necessary 'empty value' required for each field type
• Modify _get_validation_exclusions() to support excluding this condition

All of the above could have cascading consequences, and it's not clear which is the correct way forward.

Thoughts?

[Karmak23]

I have a problem which seems related.

Stacktrace: http://dev.1flow.net/development/1flow-dev/group/44097/

My code:

class Feed(Document):
    …
    thumbnail_url  = URLField(required=False, default=u'')
    …

…

class FeedAdminForm(DocumentForm):
    class Meta:
        model = Feed

It crashes, but only in the Django admin.
I use Django 1.6.
This happens whether default=u'' is present or not. Django keeps wanting to convert u'' to None and it crashes.