Question

我收到来自客户端的请求，请求需要从两个表中选择数据，从一个表我需要在表2中选择1000个记录我只需要选择两个记录，通过回调处理它。我想要在两个回调函数执行后需要发送给我的客户端的响应，如何在节点js中实现这一点？

Answer 1

欢迎回调地狱！你只需要构建pyramide表单回调！

示例：

function getDataFromDB (query, successCb, errorCb) {
    executeFirstQuery(query, function(firstQueryData) {
        console.log('First query ok! Now execute second.');

        executeSecondQuery(query, function(secondQueryData) {
            console.log('Second query ok! Now execute successCb().');

            successCb([firstQueryData, secondQueryData]);
        }, function(error) {
            errorCb("Error in second query");
        })
    }, function(error) {
        errorCb("Error in first query");
    });
}

function executeFirstQuery (query, successCb, errorCb) {
    console.log("Execute first query!");
    successCb("Some data from first query");
    // errorCb("Some Error from first query");
}

function executeSecondQuery (query, successCb, errorCb) {
    console.log("Execute second query!");
    successCb("Some from second query");
    // errorCb("Some Error from second query");
}

getDataFromDB("Some sql", function(data) {
    console.log(data);
}, function(error) {
    console.error(error);
});

或使用Promises：http://documentup.com/kriskowal/q/

Answer 2

您有以下选项：

遵循节点样式回调模式。另请阅读Callback-hell
关注promises。

回调模式

var f  = function(somedata, cb){
    // pick user from db
    pickUserFromTable1(somedata, function(err, users){
        // callled on completion of pickUserFromDB
        if(err){
            //handle error.
            cb(err, null);
            return;
        }

        pickUserFromTable2(users, function(err, finallySelectedUsers){
            // called on completion of pickUserFromTable2
            if(err){
                // handle error.
                cb(err, null);
                // returning is important. or use else part of if to separate the case
                return;
            }

            // call initiator's callback function on completion of both pickUserFromTable1 and pickUserFromTable2
            cb(null, finallySelectedUsers);
        });
    })
}

注意：这种方法适用于短项目，但如果依赖链冗长，则会导致一些维护问题（回调地狱）。

多个回调，带有一个响应-Node JS

2 个答案: