nodejs query in query result loop

Question

I'm performing mysql query using nodejs/mysql.

After the first result set, I will loop through the results set and query a second table.

1) Why 'for' works and 'foreach' doesn't? What's the proper looping way to achieve what I need?

2) item = { ...item, images: rows } in the getImage function also doesn't work, why?

3) How to let the console.log show the modified results? If I use 'await', the console.log(rows) should show the modified results right?

const getImages = async (item, key) => {
    let sql = await connection.format('SELECT * from `images` WHERE id = ?', [item.id]);
    const [ rows , fields ] = await connection.execute(sql);

    item['images'] = rows
    item = { ...item, images: rows } //'<-- this method doesn't work.

    return item
}

let sql = await connection.format(`SELECT * from table ORDER BY a.listing_id LIMIT ?,?`, [0,10])

    var [rows, fields] = await connection.execute(sql);

    // rows.forEach(getImages)   //'<-- this does not work when uncommented
    // rows = rows.forEach(getImages) //'<-- this also does not work when uncommented.

    for (let i = 0; i < rows.length; i++) {    //'<-- but this works
        rows[i] = await getImages(rows[i], i);
    }

    console.log(rows) //<----- this doesn't show modified results on terminal console
    res.json(rows) //<----- browser can see the modified results on browser console

2 years on since this question was asked, I realised that the answer below did not really answer my question. The answer to my question is simply, Foreach does not support async/await. — Someone Special
– Someone Special, Commented Aug 30, 2022 at 10:29

Juan David Ramirez Villegas · Accepted Answer · 2020-05-06 05:53:19Z

3

You have to pass to the foreach method the proper handler on each item:

let new_rows = Array()
rows.forEach(row => {
    new_rows.push(await getImages(row, i))
});

Plus, if you want to get the images on another array you should use map, its cleaner:

let new_rows = rows.map(row => {
    return await getImages(row, i)
});

answered May 6, 2020 at 5:53

Juan David Ramirez Villegas

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5 Comments

Juan David Ramirez Villegas Over a year ago

<h3> Then first, make sure the first function is working correctly: </h3> ``` ```

Juan David Ramirez Villegas Over a year ago

<h3> Then first, make sure the first function is working correctly: </h3> ``` const getImages = async (item, key) => { let sql = await connection.format('SELECT * from images WHERE id = ?', [item.id]); ... console.log(">>> Get image Return: ", item) // add this line ... } ``` <h3> Then make sure you are receiving the data: </h3> ... var [rows, fields] = await connection.execute(sql); console.log(">> Rows: ", rows) // add this line console.log(">> fields: ", fields) // add this line ... ```

Someone Special Over a year ago

my function works correctly. I will stick to for loop since there's no working .map solution

Juan David Ramirez Villegas Over a year ago

Which SQL library are you using?

Someone Special Over a year ago

I'm using mysql2 nodejs.

prasanth · Accepted Answer · 2020-05-06 05:43:45Z

0

Because forEach not returning anything .So better use Array#map

rows = rows.map(getImages)

answered May 6, 2020 at 5:43

prasanth

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