docs: function(callback){
          if(source['brokerId']!='null'){
              db.db(dbName).collection(collectionName).find({brokerId:source['brokerId']}).toArray(function(err,result){
                  mqttHost = result[0]['ipAddress'];
                  mqttPort = result[0]['port'];
                  console.log(result);
              });
          }else{
              mqttHost = mqttPort = null;
          }
      }