fileField saved in default db even after switch_db()

files are getting stored in default db even with using switch_db()

Please refer the below code that demostrates the case.
Mongo engine VERSION = 0.10.6

#models.py
from mongoengine import FileField, Document, StringField 
from mongoengine import connect, register_connection

connect('ets', alias='default')
register_connection('ets_archive','ets_archive')

class Mediafile(Document):
    content_type = StringField(max_length=255, required=True)
    file_name = StringField(max_length=1024, required=True)
    file_member = FileField( default=None)

from models import Mediafile
from mongoengine.context_managers import switch_db

def save_db():
    with switch_db(Mediafile, 'ets_archive') as Mediafile_export_db:
        mediafile = Mediafile_export_db()
        mediafile.content_type = 'text/plain'
        mediafile.file_name = 'new_db.txt'
        mediafile.file_member.new_file()
        mediafile.file_member.write('new db'.encode("UTF-8"))
        mediafile.file_member.close()
        mediafile.save()

if __name__ == '__main__':
    save_db()

When I run test.py the file is stored to the default database.
Note there Mediafile Document is still stored in the new archive database. Its only the (gridfs)file thats stored in the default database instead of database named 'ets_archive'

Start with the models.py and test.py reproduction, then inspect FileField/GridFS handling and the switch_db context manager. Verify how the database alias is selected for the document and its file. Done means both the Mediafile document and its GridFS file are stored in ets_archive rather than the default database.