3

我正在为nodejs使用优秀的caolan“异步”模块：

我有这个代码：

exports.manageComments = function(req, res) {
    var toDeleteIds = [];
    var deleteFunctions = [];
    if (req.body.doDelete) {
        toDeleteIds = req.body.doDelete;
    }
    var i;
    for ( i = 0; i < toDeleteIds.length; i++ ) {
        var deleteFunction = function(callback) {
            var id = toDeleteIds[i];
            console.log(id);
            Comment.findOne({_id:id}, function(err, found) {            
                if (!err) found.remove(callback);
            });
        }
        deleteFunctions.push(deleteFunction);
    }
    async.parallel(
        deleteFunctions,
        function(err,results) {
            exports.comments(req, res); //render a view
        }
    );
};

我的数组包含两个元素，但 console.log() 一直告诉我“未定义”。

我错过了什么？

4

3 回答 3

11

你的问题是：

    var deleteFunction = function(callback) {
        var id = toDeleteIds[i];

因为在执行每个回调函数时，i将具有与 相同的值toDeleteIds.length。闭包不会“捕获”外部变量在创建时所具有的值；它“捕获”对外部变量在执行for时所具有的任何值的引用（在这种情况下，直到循环完成之后才会出现。

In order to "trap" the value of i at the time you create your callback function, you need to make i a parameter of a function that you call to create your callback function. You need something like

    var deleteFunction = makeDeleteFunction(i, callback);

And then create a separate function outside the callback:

function makeDeleteFunction(i, callback) {
    return function(callback) {
        var id = toDeleteIds[i];
        console.log(id);
        Comment.findOne({_id:id}, function(err, found){            
            if (!err) found.remove(callback);
        });
     };
}
于 2012-09-18T10:02:08.553 回答
3

ebohlman has correctly identified the problem. However I still think creating an array of closures is hugely inefficient and unnecessary. Here's shorter, easier code to achieve the same with a single function:

exports.manageComments = function(req, res) {
    var toDeleteIds = [];
    if (req.body.doDelete) {
        toDeleteIds = req.body.doDelete;
    }

    var deleteFunction = function(id, callback) {
        console.log(id);
        Comment.findOne({_id:id}, function(err, found) {            
            if (!err) found.remove(callback);
        });
    }

    async.forEach(toDeleteIds, deleteFunction, function(err,results) {
        exports.comments(req, res); //render a view
    });
};
于 2012-09-18T22:19:22.927 回答
2

Looking at this another way, if you don't need to fire the Mongoose remove middleware on each Comment doc being removed, you can remove all identified comments in one go:

Comment.remove({_id: {$in: toDeleteIds}}, function(err, numRemoved) {
    exports.comments(req, res); //render a view        
}
于 2012-09-18T22:36:55.310 回答