Question

我在sails.js中遇到异常事件的问题。

我正在从JSONapi获取一些数据并尝试将它们写入for循环中的数据库中。一切都需要一个接一个地执行（按照正确的顺序）。为了使示例简单，我只想说我正在尝试执行以下操作：

//let apiNames be a JSON that contains some names in that order: James, Betty, Jon
//let Customer be a DB which contains that names and related age

for(index in apiNames){
   console.log("Searching for "+apiNames[index].name+" in the Database...);
   Customer.find({name:apiNames[index].name}).exec(function(err,customerData){
      console.log("Found "+apiNames[index].name+" in the Database!");
      console.log(customerData);
   });
}

建议日志应如下所示：

Searching for James in the Database....
Found James in Database!
{name:James, age:23}

Searching for Betty in the Database....
Found Betty in Database!
{name:Betty, age:43}

Searching for Jon in the Database....
Found Jon in Database!
{name:Jon, age:36}

由于Javascript以异步方式运行且数据库调用时间很长，因此输出看起来像这样：

Searching for James in the Database....
Searching for Betty in the Database....
Searching for Jon in the Database....
Found James in Database!
{name:James, age:23}
Found Betty in Database!
{name:Betty, age:43}
Found Jon in Database!
{name:Jon, age:36}

我已经尝试了几种方法来强制循环同步工作，但没有任何效果。 AFAIK如果我在exec中调用某些内容，它应该同步运行（通过链接它与另一个exec），但我的问题是，它已经失败了在循环中同步工作。有没有人有这个解决方案，可以解释一下？

编辑：apiNames不是一个数组，它是一个JSON，里面有一些数据。以下是apiNames的示例：

[{
   "name": "James",
   "gender": "male"
},
{
   "name": "Betty",
   "gender": "female"
},
{
   "name": "Jon",
   "gender": "male"
}]

（添加了性别以在json中获得更多信息。它对解决方案不重要）

Answer 1

由于apiNames是一个对象，对于IE9 +兼容性，我们可以使用Object.keys（）来获取对象中的键名，并使用它来遍历apiNames

//process all names in the array one by one
function process(apiNames, keys) {
    //if there are no items in the array return from the function
    if (!keys.length) {
        return;
    }
    //get the first name in the array
    var key = keys.shift();
    var name = apiNames[key];
    console.log("Searching for " + name + " in the Database...");
    Customer.find({
        name: name
    }).exec(function (err, customerData) {
        console.log("Found " + name + " in the Database!");
        console.log(customerData);
        //once the current item is processed call the next process method so that the second item can be processed
        process(apiNames, keys);
    });
}

//call the process method with an array
var keys = Object.keys(apiNames);
process(apiNames, keys);

对于旧版浏览器，使用polyfill添加对Object.keys（）的支持，如one provided by MDN

演示：Fiddle

Answer 2

您可以使用递归来测试布尔值，当您准备就绪时可以切换。

var isFinding = false;
var found = [];

for (index in apiNames) {
  checkIndex(index);
}

function checkIndex (index) {
  if (index) {
    found[index - 1]
    ? findCustomer(index)
    : setTimeout(checkIndex, 100, index);
  } else {
    findCustomer(index);
  }
}

function findCustomer (index) {
  if (isFinding) {
    setTimeout(findCustomer, 100, index) 
  } else {
    isFinding = true;
    console.log("Searching for "+apiNames[index]+" in the Database...");
    Customer.find({name:apiNames[index]}).exec(function(err,customerData){
      console.log("Found "+apiNames[index]+" in the Database!");
      console.log(customerData);
      found[index] = true;
      isFinding = false;
    });
  }
}

console.log("Searching for "+apiNames[index]+" in the Database...");

这是未经测试的，我半睡半醒......但我很确定这应该如你所愿......或者至少让你接近： - ）

Answer 3

因为我相信我们在这里讨论nodejs，所以我会使用async.js

和apiNames对我来说就像是阵列，如果不是那么就是

var async = require('async');

var apiNames = JSON.parse('[{"name": "James","gender": "male"},{"name": "Betty","gender": "female"}]');

async.eachSeries(apiNames, function(apiName, callback) {

  console.log("Searching for "+apiName.name+" in the Database...);

  Customer.find({name:apiName.name}).exec(function(err,customerData){
    console.log("Found "+apiName.name+" in the Database!");
    console.log(customerData);
    callback();
  });

});

在同步内部进行异步调用

3 个答案: