Issue with multiple records of the same subdocument returned for MongoDb and Python -

i'm getting strange issue when getting results of object subdocuments mongo database using python , pymongo.

i have document list of sub documents, e.g.

user: {     "_id": ....     hats: [{"colour": "blue" }] } 

i query using find_one(). returns details of document , 1 sub document record. however, next query 2 "hats", second being duplicate of first. next 3 "hats" , in continues on that.

if restart application, "count" above reset, find_one() query returns 1 sub document again.

there 1 sub document record in database, isn't issue. must doing weird in terms of in memory stuff.

i using python "tornado" framework, application tornado.wsgi.wsgiapplication. every time new request comes should opening new connection.

the request handler along lines of

class handler(requesthandler):     def initialize(self):         self.db = mongoclient("localhost", 27017) 

i'm baffled be.

ultimately nothing mongodb.

for each collection type in database had model class. decouple exact details of how data stored how returned server.

class user(modelbase):     name = none     hats = []  @staticmethod def from_db(document):     model = user()     model.name = document.get("name")      hats = document.get("hats", list())     document in hats:         hat = hat.from_db(document)         model.hats.append(hat)     return model 

the problem defined properties on model directly instead of setting in init function.

that is

class user(modelbase):     name = none     hats = [] 

instead of

class user(modelbase):     def __init__(self):         self.name = none         self.hats = [] 

i thought equivalent, seems when variables set on class directly static variables shared between instances of class. when added hat list 1 user object, next user object had hat in list , added one.