Iterate through variable containing mysql data (with javascript)

Question

I am trying to get data from mysql with javascript and then do some things with each of the results. I have saved the mysql result to a variable and thought that I could iterate through this, but I cant understand how to do it.

To make it easy I have simplified the code as below, which uses forEach():

connection.query("SELECT length, weight FROM physics WHERE user = 'Test' AND name = 'Hi'", function (err, result) { 
      if (err) throw err;
      allres = result; 

allres.forEach(function(name) {
    console.log(`I looped: ${name}`);
  });
    });

The result is:

I looped: [object Object]
I looped: [object Object]
I looped: [object Object]

If I do console.log(allres) I get:

RowDataPacket { length: '5', weight: '3' },
  RowDataPacket { length: '11', weight: '11' },
  RowDataPacket { length: '2', weight: '2' },

So the values are there, but how can I loop this?

When you do I looped: ${name}, toString() get's called on name, which for objects returns [object Object]. Instead, try accessing properties on the object, like I looped: ${name.length}, or convert the object to JSON: I looped: ${JSON.stringify(name)} — Mogzol
– Mogzol, Commented Sep 19, 2019 at 19:24

dusthaines · Accepted Answer · 2019-09-19 20:25:26Z

When you combine the object with a string it will console log everything as a string. You have a few options:

Console log the object by itself

connection.query("SELECT length, weight FROM physics WHERE user = 'Test' AND name = 'Hi'", function(err, result) {
    if (err) throw err;

    console.log('I have ' + result.length + ' results');

    result.forEach(function(entry) {
        console.log('I looped:'); // string
        console.log(entry); // object
    });
});

Console log each piece of each object

connection.query("SELECT length, weight FROM physics WHERE user = 'Test' AND name = 'Hi'", function(err, result) {
    if (err) throw err;

    console.log('I have ' + result.length + ' results');

    result.forEach(function(entry, index) {
        console.log('for entry with an index of : ' + index);
        console.log('the length value is : ' + entry.length);
        console.log('the weight value is : ' + entry.weight);
    });
});

Use the util module for nice tidy logging of nested objects

https://www.npmjs.com/package/util

var util = require('util')

connection.query("SELECT length, weight FROM physics WHERE user = 'Test' AND name = 'Hi'", function(err, result) {
    if (err) throw err;

    console.log(util.inspect(result, {showHidden: false, depth: null}));

});

CoderCharmander · Accepted Answer · 2019-09-19 19:23:06Z

1

for (let i in name) {
    let item = name[i];
    // do something with item
}

Or you can access the values directly:

let length = name.length;
let weight = data.weight;

answered Sep 19, 2019 at 19:23

CoderCharmander

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