为什么我在同一个块中得到不同的数组值？

Question

i'm using node.js as an api to my app. the thing is in this block of code i'm editing the values of the arrays inside a forEach loop but when i console.log() them i'm still getting the empty arrays. i'm thinking that the forEach loop is getting executed after the console.log() in POSITION 2 and after the response being sent. and just for the record, in POSITION 1 i'm getting the right values as i want

here's the code

router.post('/', (req, res, next) => {
    userId = req.body.userId;

    sqlQuery = `SELECT mealsids FROM tmporders WHERE userid = ${userId}`;

    con.query(sqlQuery, function (err, rows) {
        let mealsIds = [];
        let mealsNames = [];
        let mealsPrices = [];
        let mealsImages = [];
        var index = 0

        if (rows['rows'].length > 0) {
            mealsIds = rows['rows'];

            mealsIds[0]['mealsids'].forEach((row) => {

                sqlQuery2 = `SELECT name, image, price FROM meals WHERE id = ${mealsIds[0]['mealsids'][index]}`;

                con.query(sqlQuery2, function (err, rows) {
                    if (err) {
                        console.log('Failed BITCH');
                        res.sendStatus(202)
                    } else {
                        mealsNames.push(rows['rows'][0]['name']);
                        mealsPrices.push(rows['rows'][0]['price']);
                        mealsImages.push(rows['rows'][0]['image']);

                        /*   POSITION 1   */
                        console.log('============POSITION 1============');
                        console.log(mealsNames);
                        console.log(mealsPrices);
                        console.log(mealsImages);

                        /*  END OF POSITION 1   */
                    }
                });
            });

            /*   POSITION 2   */
            console.log('============POSITION 2============');
            console.log(mealsNames);
            console.log(mealsPrices);
            console.log(mealsImages);

            /*  END OF POSITION 2   */


            res.json({
                statusCode: 201,
                count: mealsNames.length,
                mealsIds: mealsIds,
                mealsNames: mealsNames,
                mealsImages: mealsImages,
                mealsPrices: mealsPrices
            })

        } else {
            console.error("Failure");
            console.log(err);
            res.sendStatus(202);
        }
    });
});

is there any way to fix this logical error?

Answer 1

Try this, it can make errors to your code, but still you can develop your code better by following this pattern.

const Query = conn => query => new Promise((resolve, reject) => {
  try {
    conn.query(query, (err, res) => {
      if (err) return reject(err)
      resolve(res.rows)
    })
  } catch (er) {
    reject(er)
  }
})

router.post('/', async (req, res, next) => {
  try {
    const query = Query(con);

    userId = req.body.userId;

    const rows = await query(`SELECT mealsids FROM tmporders WHERE userid = ${userId}`)

    if (!rows.length) {
      return res.status(202).json({
        message: '0 rows'
      })
    }

    console.log({ rows })

    mealsIds = rows.rows;

    console.log({ mealsIds })

    const meals = await mealsIds[0].mealsids.reduce((promise, e) => promise.then(async acc => {
      const currentResult = await query(`SELECT name, image, price FROM meals WHERE id = ${mealsIds[0].mealsids[0]}`)

      return acc.concat(currentResult[0])
    }), Promise.resolve([]))

    console.log({ meals })

    res.status(200).json({
      meals
    })

  } catch (err) {
    res.status(500).json(err)
  }
});

BTW, your node version has to be higher than 8.0 to run this code. Try node -v in the terminal.