I use mongoengine to connect and query to mongodb. In init, I create a connection to the db. After that, i create an instance and do some operator with db. The result of these ops is shown in termial that run the code. But when i check by mongo shell, it show nothing. How can it happen?

I check that when i create an instance of Model, there are 2 connections created. I can not find a document explaining it.

file model.py

class Model():
def __init__(self):
self.db = connect(
            db=cfg.database.db,
            host=cfg.database.host, 
            port=cfg.database.port, 
            username=cfg.database.username, 
            password=cfg.database.password,
            authentication_source='admin',
            alias=alias
        )

file main.py

from model import Model
model = Model()
# insert db ...
# get object ...
 result show here: ...

code to insert and get result

    def add(self, cid, result):
        for o_id, r in result.items():
            ObjectInfo.objects(cid=cid, o_id=o_id).update(
                push__r=r.tolist(),
                set__updatedAt=datetime.now(timezone('UTC')),
                upsert=True
            ) 
        return
    def get(self, cid):
        return ObjectInfo.objects(cid=cid)

there are currently 3 connections, including itself when init Model