whats wrong with put rows into array sqlite3 nodejs

Question

I want to save sqlite3 row values into an array. I followed what was discussed here:

Can't put rows into array using sqlite3 on Node.js

However when I console.log my would-be-array records, I obtain:

console.log(records) => an array with values [1,1,2]

console.log(records[1]) => undefined

There must be a mistake in my understanding of what's going on. What is wrong?

Full code below:

const sqlite3 = require('sqlite3').verbose();
let db = new sqlite3.Database('src/db/ksbib.db', (err) => { if (err) { return console.log(err.message); } });
let result = []; 
let records = [];

function catchResult (err, row)
{
  if (err) { return console.log(err.message); } 
  else { return result.push(row.objektid); }
}

function getData () 
{
  return new Promise ((resolve, reject) => 
  {
    db.parallelize ( () =>
    { 
      db.each(sqlTitel(param), catchResult);
      db.each(sqlAutor(param), catchResult);
    });
    resolve(result);
  })
}

async function res () 
{
  records = await getData();
  console.log(records);
  console.log(records[1]);
  return records;
};

let x = res();
console.log(x);

kirsten · Accepted Answer · 2020-03-09 00:15:41Z

The contradiction between console.log(records) and console.log(records[1]) does not exist in the commandline. It seems that some other code interferes in the console.

Moreover, the promise as implemented above resolves with the emtpy result-array before the database request is finished. One can introduce a timeout to play with the code.

In order to resolve the promise after the database request, one should resolve it in the callback function of the request. That's also the reason why db.all is much easier to handle than db.each.

Instead of a series of database requests one can then use a series of promises. Thereby it is important to wait for every single promise to be resolved (just coupling them like this return await sqr(sqlTitle(y), []).then(sqr(sqlAuthor(y), [])) gives no unique result). The result-array is completed bit by bit.

const sqlite3 = require('sqlite3').verbose();
let db = new sqlite3.Database('ksbib.db', (err) => { if (err) { return console.log(err.message); } });
let result = []; 
let p;
function sqr (sql, x)
{
    return new Promise(function (resolve, reject) 
    {
        db.all(sql, x, (err, rows) => 
        {
            if (err) { 
                reject(err); 
            } else {
                rows.forEach( (row) => {result.push(row.objektid)} );
                resolve(result);
            }
        });
    });  
}

( async () =>
{
    p = await sqr(sqlTitle(y), []);
    p = await sqr(sqlAuthor(y), []);
    return p;         //the final result
})();

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