code: function(cb){  // find first trust me ball
  				round.queryFirstTrustMEBallOnMainChainByRoundIndex(conn,objUnit.round_index, function(err,ball){
  					if(err)
  						return cb(err);
  					firstTrustMEBall = ball;
  					cb();
  				});
  			}
docs: function(cb){ round.getDifficultydByRoundIndex(conn,objUnit.round_index, function(difficulty){ if(difficulty !== payload.difficulty) return cb("Wrong difficulty detected of round " + objUnit.round_index + "expected :"+ difficulty +",actual :"+payload.difficulty); cb(); }); },