如何在 Node.js 中的下一次迭代之前使 for 循环执行所有功能

Question

每个人。我正在做一个在数据库中添加和更新文件的应用程序。 我的问题是，即使数据库更新调用仍未成功完成，我的循环仍在继续。 在继续循环之前，我如何设法使这些函数完成循环等待单元？

我们将不胜感激。

这是这段代码：

for(i = 0; i < treatments.length; i++) {
    collection3.find({"_id": parseInt(treatments[i])}).toArray(function(err, results) {
    if(results[0].maxPrice < parseInt(treatmentsPrices[i])){
        collection3.update({"_id": parseInt(treatments[i])}, {"maxPrice": parseInt(treatmentsPrices[i])}, function(err, success) {
            counter++;
            console.log(err);
        });
    }
    if(results[0].minPrice > parseInt(treatmentsPrices[i])){
        collection3.update({"_id": parseInt(treatments[i])}, {"minPrice": parseInt(treatmentsPrices[i])}, function(err, success) {
            console.log(err);
        });
    }
    collection3.update({"_id": parseInt(treatments[i])}, {$addToSet: {"doctors": parseInt(doctorId)}}, function(err, success) {
        console.log(err);
    });
    collection3.update({"_id": parseInt(treatments[i])}, {$addToSet: {"hospitals": parseInt(hospitals[i])}}, function(err, success) {
        console.log(err);
    });
    if(newHospitalName != null) {
        collection3.update({"_id": parseInt(treatments[i])}, {$addToSet: {"hospitals": parseInt(hospitalId)}}, function(err, success) {
            console.log(err);
        });
    }
    });                         
}

Answer 1

我建议您在需要执行异步操作时使用一些库。 我使用when在您的代码中编写了一个小示例，您可以看到所有方法here

var when = require('when');
var promises = [];

var treatmentsUpdater = function (opts) {
  var treatments = opts.treatments;
  var treatmentsPrices = opts.treatmentsPrices;
  var doctorId = opts.doctorId
  var hospitals = opts.hospitals;
  var hospitalId = opts.hospitalId

  collection3.find({"_id": parseInt(treatments[i])}).toArray(function(err, results) {
    if(results[0].maxPrice < parseInt(treatmentsPrices[i])){
      collection3.update({"_id": parseInt(treatments[i])}, {"maxPrice": parseInt(treatmentsPrices[i])}, function(err, success) {
        counter++;
        console.log(err);
      });
    }
    if(results[0].minPrice > parseInt(treatmentsPrices[i])){
      collection3.update({"_id": parseInt(treatments[i])}, {"minPrice": parseInt(treatmentsPrices[i])}, function(err, success) {
        console.log(err);
      });
    }
    collection3.update({"_id": parseInt(treatments[i])}, {$addToSet: {"doctors": parseInt(doctorId)}}, function(err, success) {
      console.log(err);
    });
    collection3.update({"_id": parseInt(treatments[i])}, {$addToSet: {"hospitals": parseInt(hospitals[i])}}, function(err, success) {
      console.log(err);
    });
    if(newHospitalName != null) {
      collection3.update({"_id": parseInt(treatments[i])}, {$addToSet: {"hospitals": parseInt(hospitalId)}}, function(err, success) {
        console.log(err);
      });
    }
  });
}

for(i = 0; i < treatments.length; i++) {
  var opts = {
    treatments: treatments[i],
    treatmentsPrices: treatmentsPrices[i],
    doctorId: doctorId,
    hospitals: hospitals[i],
    hospitalId: hospitalId
  }
  promises.push(treatmentsUpdater(opts))   
}

when.all(promises).then(function () {
  console.log("The database has been updated")
})

您也可以使用原生承诺：Promise.all

Answer 2

我会去无耻地宣传我们自己的图书馆Coastline。代码看起来像这样。

CL.each(treatments, function* (treatment, i) {
  
  var results = yield collection3.find({"_id": parseInt(treatment)}).toArray(CL.cb());
  
  if (results[0].maxPrice < parseInt(treatmentsPrices[i])) {
    CL.bg(collection3.update({"_id": parseInt(treatment)}, {"maxPrice": parseInt(treatmentsPrices[i])}, CL.cb()));
  }
  if(results[0].minPrice > parseInt(treatmentsPrices[i])) {
    CL.bg(collection3.update({"_id": parseInt(treatment)}, {"minPrice": parseInt(treatmentsPrices[i])}, CL.cb()));
  }
                       
  CL.bg(collection3.update({"_id": parseInt(treatment)}, {$addToSet: {"doctors": parseInt(doctorId)}}, CL.cb()));
  
  CL.bg(collection3.update({"_id": parseInt(treatment)}, {$addToSet: {"doctors": parseInt(doctorId)}}, CL.cb()));
  
  CL.bg(collection3.update({"_id": parseInt(treatment)}, {$addToSet: {"hospitals": parseInt(hospitals[i])}}, CL.cb()));
  
  if(newHospitalName != null) {
    CL.bg(collection3.update({"_id": parseInt(treatment)}, {$addToSet: {"hospitals": parseInt(hospitalId)}}, CL.cb()));
  }
  
});

库将等待所有CL.bg() 调用完成，然后再运行下一次CL.each() 迭代。您可以将CL.bg() 替换为yield，以便在迭代中按顺序执行所有内容。