Node.js-foreach中的mysql查詢

Question

我有這樣的代碼結構：

connection.query(query1,function(err,rows) {
    var response = [];
    //doing something with rows
    rows.forEach(function(item) {
        connection.query(queryItem,function(err,rows) {
            //doing something
            result = rows[0].field;
            //and want to push it to an array
            response.push(result);
        });
    });
    console.log(response); //empty
});

我知道forEach正在阻止，但查詢是非阻止的。 我試圖使用諾言：

connection.query(query1,function(err,rows) {
    var response = [];
    //doing something with rows
    rows.forEach(function(item) {
        var promise = new Promise(function(resolve,reject) {
            connection.query(queryItem,function(err,rows) {
                //doing something
                result = rows[0].field;
                //and want to push it to an array
                resolve(result);
            });
        });
        promise.then(function(result) {
            console.log(result); //ok
            response.push(result) //not ok, result is empty
        });
    });
    console.log(response); //empty
});

但這沒有幫助。 如何將值從非阻塞函數推入數組並在之后使用它？

Answer 1

創建諾言是朝正確方向邁出的一步，但是您需要進一步走一步，將諾言聚集到一個數組中並傳遞給Promise.all，然后等待它們全部完成，然后再嘗試訪問response 。

connection.query(query1,function(err,rows) {
    var response = [];
    //doing something with rows
    Promise.all(rows.map(function(item) {
        var promise = new Promise(function(resolve,reject) {
            connection.query(queryItem,function(err,rows) {
                //doing something
                result = rows[0].field;
                //and want to push it to an array
                resolve(result);
            });
        });
        return promise.then(function(result) {
            console.log(result); //ok
            response.push(result) //ok
        });
    }).then(function () {
        console.log(response); //not empty
    });
});