CODEWITHSUNDEEP
node.jspostgresqlexpress
Alexander
Alexander

Reputation: 155

async queries to database in nodeJS

I'm trying to parse file with data and insert it in the database, parsing goes well and when I make one query it runs great to, but when I trying to get this queries work in cycle it give me 

values: [output[i][0], output[i][1], output[i][2], output[i][3], o
                  ^
TypeError: Cannot read property '0' of undefined

First I was trying simple for loop but after some research about nodeJS being async I find that i need to do this in callback, but it didn't works, I think that parsing is not done by moment of starting queries routine, but I'm not sure.

var express = require('express');
var pg = require('pg');
var csv = require('fast-csv');
var app = express();

var conString = "postgres://alexzander:,tjdekma@localhost/db2015";
var output = [];

var client = new pg.Client(conString);

parser = csv.fromPath("public/dataInputOld/tblOwner.txt", {delimiter: ';'});
parser.on("data", function (data) {
    output.push(data);
});

parser.on("end", query(1));

function query(i) {
    if (i < 30) {
        client.query({
            text: 'INSERT INTO tblowner ' +
            '(intownerid, txtownersurname, txtownername, txtownersecondname, txtaddress)' +
            ' VALUES ($1, $2, $3, $4, $5)',
            values: [output[i][0], output[i][1], output[i][2], output[i][3], output[i][4]]
        }, function (err) {
            if (err) {
                console.log('error: ' + err)
            }
            else {
                console.log(i);
                query(i + 1);
            }
        });
    }
}

app.get('/', function (req, res) {
        res.send(JSON.stringify(output[1][0]));
});

var server = app.listen(3001, function () {

    var host = server.address().address;
    var port = server.address().port;

    console.log('App listening at http://%s:%s', host, port);
});

Update: now I think that i didn't connect well to database

Update2: I changed 

 parser.on("end", query(1));

to

parser.on("end", function(){
    query(1);
});

and now error is gone, but nothing inserts in database

Upvotes: 1

Views: 195

Answers (1)

Alexander
Alexander

Reputation: 155

Ended with this, sorry but I didn't understand enough about pg and getting client in it, so when i did all like in example on there docs all worked fine, thanks stackoverflow :) If I didn't try to explain this trouble to you I think I might be searching for errors a lot more time.

parser.on("end", function () {
    client.connect(function(err){
        if (err) {
            return console.error('could not connect to postgres', err);
        }
        query(1);
    });
});

function query(i) {
    if (i < 30) {
        client.query({
            text: 'INSERT INTO tblowner ' +
            '(intownerid, txtownersurname, txtownername, txtownersecondname, txtaddress)' +
            ' VALUES ($1, $2, $3, $4, $5)',
            values: [output[i][0], output[i][1], output[i][2], output[i][3], output[i][4]]
        }, function (err) {
            if (err) {
                console.log('error: ' + err)
            }
            else {
                console.log(i);
                query(i + 1);
            }
        });
    }else{
        client.end();
    }
}

Upvotes: 1

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