Question

在这个nodejs函数中，我在mongodb中创建了几条记录使用猫鼬。计数器计算了多少。

export function createTimeslots(req, res){
  var startDate = req.body.startDate;
  var Duration = req.body.Duration;
  var repeat = req.body.repeat;
  var counter=0;

  for(var i=0; i<repeat; i++){
    var startTime = ... calculation
    var endTime = ...calculation

    var ts = {
      startTime: startTime,
      endTime: endTime,
    };

    TimeSlot.create(ts, function(err, timeslot){
        counter = counter+1;
    });
  }

  res.status(200).json(counter + ' timeslots created');

}

问题是结果总是'0时隙创建'。我怀疑创建函数是异步的，到它完成时，我们不再有更新柜台了。那我怎么算这些记录呢？（我知道我可以使用循环计数器，但我打算进行验证在某些情况下不创建记录。谢谢:)）

Answer 1

Promises会在这里为您提供帮助：

export function createTimeslots(req, res){
  var startDate = req.body.startDate;
  var Duration = req.body.Duration;
  var repeat = req.body.repeat;
  var counter=0;

  var promises = [];

  for(var i=0; i<repeat; i++){
    var startTime = ... calculation
    var endTime = ...calculation

    var ts = {
      startTime: startTime,
      endTime: endTime,
    };

    promises.push(new Promise(function(resolve) {
      TimeSlot.create(ts, function(err, timeslot) {
        counter = counter+1;
        resolve();
      });
    }));
  }

  Promise.all(promises).then(function() {
      res.status(200).json(counter + ' timeslots created');
  });
}

这将等到所有异步操作都完成，然后才继续并创建返回消息。

Answer 2

每次调用createTimeslots时，

计数器都设置为0，因此将其设为模型变量

＆＃13;

var counter=0;
export function createTimeslots(req, res){
  var startDate = req.body.startDate;
  var Duration = req.body.Duration;
  var repeat = req.body.repeat;
 
  for(var i=0; i<repeat; i++){
    var startTime = ... calculation
    var endTime = ...calculation

    var ts = {
      startTime: startTime,
      endTime: endTime,
    };

    TimeSlot.create(ts, function(err, timeslot){
        counter = counter+1;
    });
  }
  
  res.status(200).json(counter + ' timeslots created');

}

＆＃13;

Answer 3

将计数器移到您传递给TimeSlot创建方法的异步回调体外。

export function createTimeslots(req, res){
  var startDate = req.body.startDate;
  var Duration = req.body.Duration;
  var repeat = req.body.repeat;
  var counter=0;


  for(var i=0; i<repeat; i++){
    var startTime = ... calculation
    var endTime = ...calculation

    var ts = {
      startTime: startTime,
      endTime: endTime,
    };

    counter = counter+1;

    TimeSlot.create(ts, function(err, timeslot){
        // do stuff with counter

    });
  }

  res.status(200).json(counter + ' timeslots created');

}

nodejs异步调用循环

3 个答案: