Select specific fields from collection within collection in mongodb c# -

i have collection of person in mongodb has structure this:

class person {    public string { get; set; }    public address houseaddress { get; set; } }  class address {    public string streetnumber { get; set; }    public city currentcity { get; set; } }  class city {    public string name { get; set; } } 

i want select city subfield of person. tried using excluding , including not working. tell me correct way in c#

i have tried code:

string jsonquery = @"{}, {'houseaddress.currentcity' : 1, _id:0}";  bsondocument query = mongodb.bson.serialization.bsonserializer.deserialize<bsondocument>(jsonquery); var squery = new querydocument(query); var cities = dbconnection.person.findas<person>(squery).setfields(fields.include("currentcity"));