如何将函数的值传递给async.waterfall函数

Question

I have a problem with my code. I want to select from a Mysql table and considering the result, change it and update that table again. Problem is, the code do this asynchronous and it won't work properly (it do all SELECT first and all of UPDATE after). So I used async.js to get the job done, but still not working. Because I cant pass the Selected value out of caller callback. So it is not possible to pass it to next callback via async.waterfall. Any ideas?

async.waterfall([

    function (callback) {

        queryBuilder.selectAgent(connection, id, (agent) => {
            // Here is the PROBLEM! I can't pass agent out of this
        });

        // Here agent will be undefined
        callback(null, agent);
    },

    function (agent, callback) {

        if (agent) {
            // Some change on agent and pass it to next callback
        }

        callback(null, agent);
    },

    function (agent, callback) {

        queryBuilder.updateAgent(connection, id, agent);

        callback(null);
    },

],

function (err) {
    if (err) throw err;

})

Answer 1

您需要在updateAgent方法中进行更改，以检查先前的值并向其中添加新数据，或者您可以先检查任何特定项目的更新，然后收集它们以一次更新该字段。