mongoEngine miss the filed when the value is null after save

Question

Here is a sample document:

{"id":1,
"info":{"age":10,"grade":80,"address":"LA"}
}

What I did:

# query the document
student = Student.objects(id=1).first()
# change the info
student.info['address'] = None
# save the change
studen.save()

When I look at the db, this document miss the address field. the info is {"age":10,"grade":80} Why save() operation can auto miss the null field, how to avoid it? (I know use update can keep the null field, but can I use save and still keep the null field?)

Answer 1

You can either try to give it Nan or void string ""

student.info = {"age":10,"grade":80,"address":""}

or

student.info = {"age":10,"grade":80,"address":Nan}