Question

这是一个更普遍的JS问题，并不是特定于edge.js.我想通过edge.js玩SQL Server访问。基于the following snippet from its GitHub site

var edge = require('edge');

var getTop10Products = edge.func('sql', function () {/*
    select top 10 * from Products
*/});

getTop10Products(null, function (error, result) {
    if (error) throw error;
    console.log(result);
    console.log(result[0].ProductName);
    console.log(result[1].ReorderLevel);
});

我写了以下内容来访问我自己的数据库：

var edge = require('edge');
var _    = require('lodash');


var thingsAccess = function () {/*
    select * from Things where Status = 'A' and Type=@thingType 
*/};

var getThingsList = edge.func('sql', thingsAccess);

var logResult = function (error, result) {
    if (error) throw error;

    _.each(result, function (thing) {
        console.log(thing.Id, thing.Category, thing.Name);
    });
};

var thingsOfType = function (type) {
    return function () { 
        getThingsList({ thingType: type }, logResult); 
    };
};


var xThings = thingsOfType('X');
var yThings = thingsOfType('Y');


xThings();
yThings();

我的问题是，如何从logResult返回结果而不仅仅是使用该函数中的数据？而不是现在登录到控制台的_.each(result, ...)构造，而是像return _.map(result, ...)那样返回Thing对象的数组。但是因为函数是getThingsList的回调函数，所以无处可放。

鉴于我如何构造代码，似乎我唯一的选择是在外部作用域中声明一个数组并从logResult内部推送到它。我确定我做错了，但我看不出如何重组。有什么建议吗？

Answer 1

你不能＆＃34;返回＆＃34;它，你必须在回调中工作，就像日志功能一样。

var thingsOfType = function (type, onSuccess, onError) {
    getThingsList({ thingType: type }, function (error, result) {

        // Process if no error
        if (!error) {
            if (onSuccess instanceof Function) {
                onSuccess(result);
            }
            // silently do nothing if onSuccess is not a function
            return;
        }

        // Handle errors using the onError callback or throw
        if (onError instanceof Function) {
            onError(error, result);
            return;
        }

        // unhandled errors
        throw error;

    }); 
};

现在您可以将它用作数组或在每个数据库中使用：

thingsOfType("X", function (result) {

    // Here result should be an Array
    var len = result.length;

    // You can use result here with or without _.each

    // Do something here

} /*, not an onError function defined */ );

示例用法，以及如何进一步使用事件驱动代码：

var printAllThingsOf = function (type, onSuccess, onError) {

   thingsOfType(type, function (result) {

       // Print each one
       _.each(result, function (thing) {
           console.log(thing.Id, thing.Category, thing.Name);
       });

       // this function is the thingsOfType-onSuccess function,
       // so propagate the new printAllThingsOf-onSuccess function;
       // "call the callback"
       if (onSuccess instanceof Function) {
           onSuccess(result);
       }

   }, onError /* propagate the onError */ );

};

printAllThingsOf("X"); // just do it or fail. onSuccess and onError are undefined.

如何从edge.js func访问MSSQL返回数据？

1 个答案: