using MongoDB.Bson;
using MongoDB.Driver;

var info_id = Query.EQ("_id", "1");
IMongoUpdate info_up = Update.Set("qPosition","2");
cinfo.Update(info_id, info_up);

var info_id = Query.EQ("_id", "2");
IMongoUpdate info_up = Update.Set("qPosition","1");
cinfo.Update(info_id, info_up);