Please recall fix on: Saving document doesn't create new fields in existing collection #620

[iici-gli]

The fix #620 has a bug. The key for changed_fields should not be field_name. It should use db_field.
When a ListField is missed in database and the field has a db_field is different than the field name, the default value check can put wrong field back to database. Then the database will no longer work.
It is better to take out whole block starting on 'elif field.default:', at line 713. Mongoengine should not change database silently.
The bug is in this code:
elif not only_fields or field_name in only_fields:
changed_fields.append(field_name)

test:

In old time you can have this:

class User(Document):
username = StringField(unique=True, db_field='unm')
password = StringField(db_field='pss')

supper_name = User(username='admin', password='admin')
supper_name.save()

Then you may add some communication information to it:

class User(Document):
username = StringField(unique=True, db_field='unm')
password = StringField(db_field='pss')
communication_information_list = ListField(StringField(), db_field='com_ls')

new_user = User(username='a_user', password='auser', communication_information_list=
['phone: 234 765 1324', 'email: [email protected]'])
new_user.save()

load supper_user back

su = User.objects(username='admin').first()
print su._change_fields

You will see 'communication_information_list ' in changed list instead of 'com_ls'

change the password, then save, in database 'communication_information_list ' : null will be inserted

su.password = 'root'
su.save()

load it back, it will crash

su = User.objects(username='admin').first()

[bagerard]

closing this, tried the snippet and Issue seemed to have been fixed