var sender_username = req.session.user_id;
var recipient_username = req.body.recipient_username;
var content = req.body.content;
var sql = ' SELECT sender_username, recipient_username, COUNT(recipient_username) as count FROM message WHERE sender_username = "'+sender_username+'" AND recipient_username = "'+recipient_username+'" GROUP BY sender_username LIMIT 1 ';
var message_no = 0;
var data;
connection.query(sql, function(err, result) {
if (err) {
res.send(err);
}
else {
data = result;
// res.send(data); < - this works
// res.send(result); <- this works
// res.send(result.count); <- undefined
}
});
res.send(data); // undefined (can't seem to save to variable after connection.query())
The res.send(result); seems to work. It gives:
[{"sender_username":"sender","recipient_username":"recipient","count":2}]
I am just trying to get the value for count and save that to a variable, but things like result.count are returning undefined for some reason.
It's because the JSON is an array, so you should access it like the following
res.send(result[0].count);
Related
The nodejs code below works fine when used to retrieve content from database. now when i tried to get content via pagination as per code below via prepared query statement
db.query('SELECT * FROM posts1 limit row=?, rowperpage=?', [parseInt(row),parseInt(rowperpage)], function (error, results, fields) {
});
it returns error "cannot read property forEach of undefined"
below is the full code
exports.display = function (req, res) {
var row = 0;
var rowperpage = 3;
console.log(row);
console.log(rowperpage);
var objs1 = [];
db.query('SELECT * FROM posts1 limit row=?, rowperpage=?', [parseInt(row),parseInt(rowperpage)], function (error, results, fields) {
// db.query('SELECT * FROM posts1', function (error, results, fields) {
results.forEach(function(row) {
var id = row.id;
var title = row.title;
var content = row.content;
var shortcontent = row.content;
var link = row.link;
objs1.push({
id: id,
title: title,
shortcontent: shortcontent,
content: content,
link: link,
});
});
res.end(JSON.stringify(objs1));
});
}
Adding the following code below, solve the issue
//parse int Convert String to number
let startNum = parseInt(row);
let LimitNum = parseInt(rowperpage);
var objs1 = [];
db.query("SELECT * FROM ?? limit ? offset ?", ["posts1",LimitNum,startNum], function (error, results, fields) {
Thanks
I am working with NodeJS using ExpressJS framework in a mysql backend. I am running a query inside a for loop and my loop and work afterwards depends on the return value of the query. I am not very good with mysql query so I am running it through a for loop.
The problem is, due asynchronous [I guess!], the for loop ends long before the query result comes out.
Here is my code:
function search_people_step2(user_id, search_criteria, user_friend)
{
var first_name_friends = [];
var last_name_friends = [];
for(var i = 0; i < user_friend.length; i++)
{
con.query("SELECT first_name, second_name FROM user WHERE userid = ?", user_friend[i],function(err, rows)
{
if(err)
{
//error;
}
else
{
if(rows.length == 0)
{
//nothing gets returned
}
else {
console.log(rows);
first_name_friends[i] = rows[0].first_name;
last_name_friends[i] = rows[0].second_name;
}
}
});
}
Now,I can get the value (using console.log) inside the query statement, however, on the outside, the value becomes empty (undefined) since the rest of the code has already been computed.
How can I solve this?
Thanks in advance.
The first thing that I find weird in your code is that you are not using an IN statement in your SQL query (not directly related to your problem though) which means you are making as many requests as there are entries in user_friend. The problem is that the SQL library is implemented asynchronously and you cannot avoid it. BUT you can handle it elegantly with Promises which are ES6 features:
(I didn't test the code but I think it should work)
function search_people_step2(user_id, search_criteria, user_friend)
{
return new Promise((resolve,reject)=>{
var first_name_friends = [];
var last_name_friends = [];
var placeHolders=user_friend.map(()=>"?").join(",");
con.query("SELECT first_name, second_name FROM user WHERE userid IN ("+placeHolders+")",user_friend,(err,rows)=>{
if(err)
reject(err);
else{
rows.forEach(row=>{
first_name_friends.push(row.first_name);
last_name_friends.push(row.second_name);
});
resolve({first_name_friends,last_name_friends});
}
});
});
}
And call your function like this :
search_people_step2(id,crit,friends).then(result=>{
//handle result asynchronously as there is no choice
console.log(result.first_name_friends);
console.log(result.last_name_friends);
}).catch(err=>{
//handle error
});
You are right, your problem is the asynchronous nature of the mysql call. You have to provide a callback to your search_people_step2 function.
You may change it like this:
search_people_step2(user_id, search_criteria, user_friend, callback)
In your function body you may use a library called async to handle all the callbacks properly. Here is an example for the usage:
async.eachSeries(user_friend, function(item, eachCb){
con.query("SELECT first_name, second_name FROM user WHERE userid = ?",
user_friend[i],function(err, rows) {
if(err) {
eachCb('error');
}
else {
if(rows.length == 0){
//nothing gets returned
eachCb(null);
}
else {
console.log(rows);
first_name_friends.push(rows[0].first_name);
last_name_friends.push(rows[0].second_name);
eachCb(null);
}
}
}, callback);
});
This calls each query in order on every item of the array and calls the inner callback if finished. When all items are processed or an error occured the outer callback is called. See the async library for further documentation.
simplest solution is
function search_people_step2(user_id, search_criteria, user_friend)
{
var first_name_friends = [];
var last_name_friends = [];
for(var i = 0; i < user_friend.length; i++)
{
con.query("SELECT first_name, second_name FROM user WHERE userid = ?", user_friend[i],function(err, rows)
{
if(err)
{
//error;
}
else
{
if(rows.length == 0)
{
//nothing gets returned
}
else {
console.log(rows);
first_name_friends[i] = rows[0].first_name;
last_name_friends[i] = rows[0].second_name;
}
if(i==user_friend.length-1){
//do your work here which you want to perform in end
}
}
});
}
or use async library
var async = require('async');
var first_name_friends = [];
var last_name_friends = [];
async.series([function(cb){
function search_people_step2(user_id, search_criteria, user_friend)
{
for(var i = 0; i < user_friend.length; i++)
{
con.query("SELECT first_name, second_name FROM user WHERE userid = ?", user_friend[i],function(err, rows)
{
if(err)
{
//error;
}
else
{
if(rows.length == 0)
{
//nothing gets returned
}
else {
console.log(rows);
first_name_friends[i] = rows[0].first_name;
last_name_friends[i] = rows[0].second_name;
}
if(i==user_friend.length-1){
cb()
}
}
});
}
},function(cb){
//do your work here
}],function(err){})
I'm trying to run this piece of code:
setInterval(function () {
var params = {
QueueUrl: 'https://sqs.us-east-1.amazonaws.com/821808622769/Teste', // required
MaxNumberOfMessages: 10
};
sqs.receiveMessage(params, function (err, data) {
if (err)
console.log('Erro de SQS:' + err);
else {
var retorno = data.Messages;
for (var i in data.Messages) {
var queryString = 'SELECT now()'; //dummy query, just for tests
db_connection.query(queryString, null, function (err, rows, fields) {
if (err) {
console.log('Erro no BD:' + err);
return;
}
var date = new Date();
console.log(retorno[i].Body + ' ' + date.getTime().toString());
});
}
console.log();
}
});
}, 30000);
and I have 5 messages in AWS SQS, such as this:
but when I run my code, instead of having the retorno[i].Body of each message, sometimes I get a message repeated, as show in this image
My for loop is running from 1 to 5 queries, but how do I carry the retorno[i] inside the callback to the database query? I mean, how do I identify which message I was dealing with?
Using .bind() you can setting the internal version of i to be the same as the version of i in your loop.
.bind({i:i}) at the end of your callback and change the internal code to reference this.i
for (var i in data.Messages) {
var queryString = 'SELECT now()'; //dummy query, just for tests
db_connection.query(queryString, null, function(err, rows, fields) {
if (err) {
console.log('Erro no BD:' + err);
return;
}
var date = new Date();
console.log(retorno[this.i].Body + ' ' + date.getTime().toString());
}.bind({
i: i
});
}
}
This question already has answers here:
How do I return the response from an asynchronous call?
(41 answers)
Why is my variable unaltered after I modify it inside of a function? - Asynchronous code reference
(7 answers)
Closed 1 year ago.
im trying to save the result of MySql query in variable using node-mysql model and node.js so i have this code:
connection.query("select * from ROOMS", function(err, rows){
if(err) {
throw err;
} else {
console.log(rows);
}
});
and the result is :
[ { idRooms: 1, Room_Name: 'dd' },
{ idRooms: 2, Room_Name: 'sad' } ]
so i need to store this results in variable so i try like this:
var someVar = connection.query("select * from ROOMS", function(err, rows){
if(err) {
throw err;
} else {
return rows;
}
});
console.log(someVar);
but is not working thanks for any help in advance.
Well #Fadi, connection.query is async, which mean when your call your console.log(someVar), someVar has not been set yet.
What you could do:
var someVar = [];
connection.query("select * from ROOMS", function(err, rows){
if(err) {
throw err;
} else {
setValue(rows);
}
});
function setValue(value) {
someVar = value;
console.log(someVar);
}
You can't do that because network i/o is asynchronous and non-blocking in node.js. So any logic that comes afterwards that must execute only after the query has finished, you must place inside the query's callback. If you have many nested asynchronous operations you may look into using a module such as async to help better organize your asynchronous tasks.
As a complement to already given answers.
var **someVar** = connection.query( *sqlQuery*, *callback function( err , row , fields){}* )
console.log(**someVar**);
This construction will return in someVar information of this connection and his SQL query . It will not return values from the query .
Values from the query are located in the callback function ( err , row , fields)
Here is your answer if you want to assign a variable to res.render
//before define the values
var tum_render = [];
tum_render.title = "Turan";
tum_render.description = "Turan'ın websitesi";
//left the queries seperatly
var rastgeleQuery = "SELECT baslik,hit FROM icerik ORDER BY RAND() LIMIT 1";
var son5Query = "SELECT baslik,hit FROM icerik LIMIT 5";
var query_arr = [rastgeleQuery, son5Query];
var query_name = ['rastgele', 'son5'];
//and the functions are
//query for db
function runQuery(query_arr,sira){
connection.query(query_arr[sira], function(err, rows, fields) {
if (err) throw err;
var obj = [];
obj[query_name[sira]] = rows;
sonuclar.push(obj);
if (query_arr.length <= sira+1){
sonuc();
}else{
runQuery(query_arr, sira+1);
}
});
}
//the function joins some functions http://stackoverflow.com/questions/2454295/javascript-concatenate-properties-from-multiple-objects-associative-array
function collect() {
var ret = {};
var len = arguments.length;
for (var i=0; i<len; i++) {
for (p in arguments[i]) {
if (arguments[i].hasOwnProperty(p)) {
ret[p] = arguments[i][p];
}
}
}
return ret;
}
//runQuery callback
function sonuc(){
for(var x = 0; x<=sonuclar.length-1; x++){
tum_render = collect(tum_render,sonuclar[x]);
}
console.log(tum_render);
res.render('index', tum_render);
}
I have an issue with extracting value from object. I want to check if my SQL table have the asked row:
var checkRow = function(connection,chekedColumn,chekParam, checkVal){
connection.query('SELECT EXISTS(SELECT '+ chekedColumn +' FROM asterisk.users where ' +chekParam+'='+checkVal+')', function (err, rows) {
if(err) console.log('SQL suerry error')
else {
console.log(rows[0]); // output: { 'EXISTS(SELECT id FROM asterisk.users where name=1600)': 1 }
return (rows[0]);
};
});
};
but returned value from query is an object, and return(rows[0]) give just [object object] output. How can I extract value of this object?
You can use
Object.keys(obj)
to get the values of the object. See api reference for more info.
EDIT:
Just to elaborate abit more on this... how you'd go about getting it out is this.
// get the keys of the source
var keys = Object.keys( source );
// loop through the keys
for ( var i = 0; i < keys.length; i++ ) {
var key = keys[i];
var value = source[key];
//do something with value
}
The output is an object which you don't know. So try either:
console.log("Result: %j", rows[0]);
console.log(JSON.stringify(rows[0]));
console.log(require('util').inspect(rows[0], false, null));
to view the structure. After you know the keys, use it to access the data.
Thanks all for helps and for your ideas. Dmitry Matveev help me to understand how to identify object properties(Objekt.keys()). And thanks to user568109 for reminding of asynchronous function, so I use callback. Final code:
var checkRow = function(connection,chekedColumn,chekParam, checkVal,callback){
connection.query('SELECT EXISTS(SELECT '+ chekedColumn +' FROM asterisk.users where ' +chekParam+'='+checkVal+')', function (err, rows) {
if(err) console.log('SQL suerry error')
else {
var keys=Object.keys(rows[0]);
keys.forEach(function(key) {
callback(rows[0][key]);
});
};
});
};
And for using this functions we need to call it like:
checkRow(connection,'id','name',name,function(value){
console.log(value)
})