在同步內進行異步調用

Question

我在sails.js中的異步事件中遇到了一些問題。

我從JSONapi獲取一些數據，並試圖將它們寫入到for循環中的數據庫中。一切都需要一個接一個地執行（以正確的順序）。爲了簡化這個例子只是可以說，我試圖做到以下幾點：

//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); 
    }); 
} 

的建議日誌應該是這樣的：

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} 

由於JavaScript是異步運行，DB調用抽空長，輸出看起來像這樣：

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} 

我已經嘗試了幾件事情來強制循環同步工作，但沒有任何工作。 AFAIK如果我在exec內部調用某個東西，它應該同步運行（通過與另一個exec鏈接），但是我的問題是，它在循環中同步工作已經失敗。有沒有人有這個解決方案，可以解釋一下？

編輯：apiNames不是一個數組，它是一個JSON，裏面有一些數據。這裏是apiNames怎麼看起來像一個例子：（由性別有在JSON的一些詳細信息，它不重要的解決方案）

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

Answer 1

由於apiNames是一個對象，IE9 +的兼容性，我們可以使用Object.keys（）來獲取該對象中的鍵名，並用它來遍歷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); 

舊的瀏覽器使用填充工具以增加對Object.keys（支持）之類的one provided by MDN

演示：Fiddle

Answer 2

您可以使用遞歸來測試布爾值，您可以在準備就緒時進行切換。

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..."); 

這是未經測試，我半睡半醒的......但我敢肯定這應該工作你想怎麼...或者至少讓你接近:-)

Answer 3

因爲我相信我們談論這裏的NodeJS我會用async.js

和apiNames看起來像數組給我，如果它不是那麼讓它

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(); 
    }); 

});