I am new to javascript and i am having trouble solving this error. I get the message: "callback is not a function" at:"return callback(rolesArray)".
Rol.getAllRoles = function(callback){
sql = "select role from Role;";
var rolesArray = [];
var role;
mysql.connection(function(err,conn){
if (err){
return callback(err);
}
conn.query(sql,function(err,rows){
if (err){
return callback(err);
}
for(var i=0; i < rows.length; i++){
role = rows[i].role;
rolesArray.push(rol);
}
console.log("roles: " + rolesArray);
return callback(rolesArray);
});
});
}
The console.log outputs:"roles: admin,customer" so the connection with the database works.
That error means that you are not passing a function to Rol.getAllRoles(fn) when you call it.
In addition, so that you can have proper error handling in your callback and so you can more easily distinguish between an error and the actual data, you should always pass a first argument to the callback that indicates whether there was an error or not and then the second argument (if not an error) can be your results array like this:
Rol.getAllRoles = function(callback){
sql = "select role from Role;";
var rolesArray = [];
var role;
mysql.connection(function(err,conn){
if (err){
return callback(err);
}
conn.query(sql,function(err,rows){
if (err){
return callback(err);
}
for(var i=0; i < rows.length; i++){
role = rows[i].role;
rolesArray.push(rol);
}
console.log("roles: " + rolesArray);
// make sure the first argument to the callback
// is an error value, null if no error
return callback(null, rolesArray);
});
});
}
And, then you should be calling it like this:
Rol.getAllRoles(function(err, rolesArray) {
if (err) {
// handle error here
} else {
// process rolesArray here
}
});
This style of calling an async callback as in callback(err, data) is a very common async callback design pattern. It allows all callers to see if there was an error or not and if there was no error to get access to the final result.
I'd suggest the following:
Rol.getAllRoles = function(callback){
var sql = "select role from Role;";
var rolesArray = [];
var role;
callback = callback || function(){};
mysql.connection(function(err,conn){
if (err){
return callback(err);
}
conn.query(sql,function(err,rows){
if (err){
return callback(err);
}
for(var i=0; i < rows.length; i++){
role = rows[i].role;
rolesArray.push(rol);
}
console.log("roles: " + rolesArray);
return callback(rolesArray);
});
});
}
This way you enforce that callback is always a function. If you run it like Rol.getAllRoles() then you would get an error previously. Now you wont. You wont get any data back though.
Make sure you are calling Rol.getAllRoles with the proper parameter (ie: a function).
Related
I am trying to build login system using node.js and i am stuck in this call back function error i have managed to build get login info and check them with data base but when i am verifying password it's taking some time so in there i need to use call back function but even i used callback function it's giving me the same error which is since validation or database call taking time it's executing other stuff in the in my case if conditions.
i have tried to implement this another way just tried to console.log order and all executing opposite this my result first
this is the order that it's run
3
2
undefined
1
but i need run this exactly opposite should i use promises instead of callback?
const {ipcMain} = require('electron');
const Password = require("node-php-password");
const connection = require("./connection");
var hash;
var done;
var self = module.exports = {
getuser_information:function(user_name,pwd,callback){
connection.query("SELECT * FROM `super_admin` WHERE ad_un = ?", user_name, function(err, result, fildes) {
if (err) throw err;
let numbers_retuned = result.length;
hash = result[0].desk;
console.log(1);
});
callback(hash,self.true_or_not);
},
hashverif:function(hash,true_or_not){
true_or_not();
console.log(2);
},
true_or_not:function(){
console.log(3);
return 1
}
}
UPDATE after your comment
You have two errors
Your get_stored_password function returns nothing when your callback function is called that's why console.log(function_returning_nothing()) outputs undefined
You forgot to pass done to your callback function in
get_stored_password's definition callback(done)
const {
ipcMain
} = require('electron');
const Password = require("node-php-password");
const connection = require("./connection");
var hash;
var done;
var self = module.exports = {
get_stored_password: function(name, pwd, callback) {
connection.query("SELECT * FROM `super_admin` WHERE ad_un = ?", name, function(err, result, fildes) {
if (err) throw err;
let numbers_retuned = result.length;
hash = result[0].desk;
if (numbers_retuned == 1) {
var test = pwd;
done = Password.verify(test, hash);
} else {
console.log('no');
return 0;
}
//you must pass an argument to your callback function
// and return done var to get an output when you log this function
callback(done);
return done;
});
},
chek_if_true: function(done) {
console.log(done);
if (done) {
return true;
} else {
return false;
}
}
}
That's why when you log done to the console it's undefined
I am unable to capture a variable into the lambda function from its outer scope. When I run this code it executes with the same variable. I am passing the variable into the function, but I am obviously misunderstanding how scoping works with lambda.
// Add tasks to async_tasks
for(var i = 0; i < 10; i++){
var task = function(task_callback){
// I want to capture i and pass it to the function
(function(i){
exports.defaultCarWithId(connection, i, function(err, data){
if (err) {
console.log('error in query: ' + err.stack);
fCallback("[Internal Server Error]", null);
return;
}
task_callback();
});
})(i);
};
async_tasks.push(task);
}
// execute tasks
async.parallel(async_tasks, function(err, results){
fCallback(null, user);
return;
});
You can wrap the outer function:
var task = (function(i){
return function(task_callback){
exports.defaultCarWithId(connection, i, function(err, data){
if (err) {
console.log('error in query: ' + err.stack);
fCallback("[Internal Server Error]", null);
return;
}
task_callback();
});
};
})(i);
async_tasks.push(task);
or pass i as argument and bind it:
var task = function(i, task_callback){
exports.defaultCarWithId(connection, i, function(err, data){
if (err) {
console.log('error in query: ' + err.stack);
fCallback("[Internal Server Error]", null);
return;
}
task_callback();
});
};
async_tasks.push(task.bind(null, i));
Basically two mistakes i can see:
You are re-declaring the variable i inside for loop. Name it something different.
Create closure something like this:
Var task = (function(i) {
return function(task_callback) {
// Your logic
};
})(i);
Hope it'll help.
It's hard to understand what exactly you are calling lambda here but if you want to bind context in async you need to use method each or one of new array methods of a framework. Have a look to docs
I am trying to get my head around this non-blocking business.
Can you tell me what i am doing wrong here? I have tried to add a retrieveContactName function which gets more information from the db before writing to socket. I have tried to make it a callback but i get the error at bottom.
case 'getConversations':
var sip = parts[1];
var pass = parts[2].replace(/[\n\r]/g, ''); //strip that carriage return
var sql = "SELECT DISTINCT(session) FROM im WHERE sip = "+connection.escape(sip)+" AND password = "+connection.escape(pass)+" ORDER BY timestamp DESC";
connection.query(sql, function(err, results) {
if (err) winston.warn(err);
for (var i=0; i < results.length; i++) {
retrieveContactName(results[i].session, sip, pass, function(value) {
sock.write('Conversations '+results[i].session+' '+value+'\n');
});
}
});
break;
elsewhere
function retrieveContactName(session, user, pass, callback) {
var sql = "SELECT `im_from` FROM `im` WHERE `session` = "+connection.escape(session)+" AND `im_to` != "+connection.escape(session)+" AND `sip` = "+connection.escape(user)+" AND `password` = "+connection.escape(pass)+" LIMIT 1";
connection.query(sql, function(err, results) {
if (err) winston.warn(err);
if (results.length > 0 ) {
callback(results[0].im_from);
} else {
callback(session.replace("contact:",""));
}
});
}
and my error
TypeError: Cannot read property 'session' of undefined
at /home/ubuntu/socket/server.js:44:47
at Query._callback (/home/ubuntu/socket/server.js:79:4)
at Query.end (/home/ubuntu/socket/node_modules/mysql/lib/protocol/sequences/Sequence.js:75:24)
at Query._handleFinalResultPacket (/home/ubuntu/socket/node_modules/mysql/lib/protocol/sequences/Query.js:143:8)
at Query.EofPacket (/home/ubuntu/socket/node_modules/mysql/lib/protocol/sequences/Query.js:127:8)
at Protocol._parsePacket (/home/ubuntu/socket/node_modules/mysql/lib/protocol/Protocol.js:172:24)
at Parser.write (/home/ubuntu/socket/node_modules/mysql/lib/protocol/Parser.js:62:12)
at Protocol.write (/home/ubuntu/socket/node_modules/mysql/lib/protocol/Protocol.js:37:16)
at Socket.ondata (stream.js:38:26)
at Socket.emit (events.js:88:20)
Your problem is down to not fully understanding scope, basically the issue is occurring here:
for (var i=0; i < results.length; i++) {
retrieveContactName(results[i].session, sip, pass, function(value) {
sock.write('Conversations '+results[i].session+' '+value+'\n');
});
}
The above will not work as you expect, all because by the time your callback fires i will not have the value you expect... it will most likely be equal to results.length which will give you an undefined slot in results. This is because the for will most likely have continued on and finished it's execution before the callbacks ever occur. This is the principal of non-blocking, code does not wait, it carries on, and your callbacks have to be prepared for this.
In order to use the value of i, or any variable that may change it's value outside the scope of your callback, you need to capture that value and store it with your callback. There are a few ways to do this but the nicest way is to pass the data your callback requires in as arguments — so you need to pass the results[i].session (passed into retrieveContactName) on to your callback.
function retrieveContactName(session, user, pass, callback) {
var sql = "SELECT `im_from` FROM `im` WHERE `session` = "+connection.escape(session)+" AND `im_to` != "+connection.escape(session)+" AND `sip` = "+connection.escape(user)+" AND `password` = "+connection.escape(pass)+" LIMIT 1";
connection.query(sql, function(err, results) {
if (err) winston.warn(err);
if (results.length > 0 ) {
callback(results[0].im_from, session);
} else {
callback(session.replace("contact:",""), session);
}
});
}
And then:
for (var i=0; i < results.length; i++) {
retrieveContactName(results[i].session, sip, pass, function(value, session) {
sock.write('Conversations '+session+' '+value+'\n');
});
}
Obviously this is just a quick example, it may be best to pass in the actual result row — depending on what you want / need.
results[i] may be out of scope inside the callback
case 'getConversations':
var sip = parts[1];
var pass = parts[2].replace(/[\n\r]/g, ''); //strip that carriage return
var sql = "SELECT DISTINCT(session) FROM im WHERE sip = "+connection.escape(sip)+" AND password = "+connection.escape(pass)+" ORDER BY timestamp DESC";
connection.query(sql, function(err, results) {
if (err) winston.warn(err);
for (var i=0; i < results.length; i++) {
retrieveContactName(results[i].session, sip, pass, function(value) {
sock.write('Conversations '+results[i].session+' '+value+'\n');
});
}
});
break;
can you place a console.log(results) just above:
sock.write('Conversations '+results[i].session+' '+value+'\n');
NEW POST:
Here is the sample of the working async code without a db.
The problem is, if i replace the vars (data1_nodb,...) with the db.collection.find();
function, all needed db vars received at the end and the for() loop ends not
correct. I hope that explains my problem a bit better. OA
var calc = new Array();
function mach1(callback){
error_buy = 0;
// some vars
for(var x_c99 = 0; x_c99 < array_temp_check0.length;x_c99++){
// some vars
calc[x_c99] = new Array();
calc[x_c99][0]= new Array();
calc[x_c99][0][0] = "dummy1";
calc[x_c99][0][1] = "dummy2";
calc[x_c99][0][2] = "dummy3";
calc[x_c99][0][3] = "dummy4";
calc[x_c99][0][4] = "dummy5";
function start_query(callback) {
data1_nodb = "data1";
data2_nodb = "data2";
data3_nodb = "data3";
data4_nodb = "data4";
calc[x_c99][0][0] = data1_nodb;
calc[x_c99][0][1] = data2_nodb;
calc[x_c99][0][2] = data3_nodb;
callback(data1_nodb,data2_nodb,etc..);
}
start_query(function() {
console.log("start_query OK!");
function start_query2(callback) {
data4_nodb = "data5";
data5_nodb = "data6";
data6_nodb = "data7";
calc[x_c99][0][3] = data4_nodb;
calc[x_c99][0][4] = data5_nodb;
callback(data5_nodb,data6_nodb,etc..);
}
start_query2(function() {
console.log("start_query2 OK!");
function start_query3(callback) {
for(...){
// do something
}
callback(vars...);
}
start_query3(function() {
console.log("start_query3 OK!");
});
});
});
}
callback(calc);
};
function mach2(callback){
mach1(function() {
console.log("mach1 OK!");
for(...){
// do something
}
});
callback(calc,error_buy);
};
mach2(function() {
console.log("mach2 OK 2!");
});
OLD POST:
i try to read data from the mongodb and send them back with a callback to the next
function, that needs the infos from the db to proceed.
Without the mongodb read functions it works perfect but now i dont know how
i can send the db vars out of the two inner functions to the first callback function.
Hope someone can help me...
Thanks
var error = 0; var var1 = "yessir";
function start_query(callback) {
var db_name = "db1";
db[db_name].find({name:var1},{data1:1, data2:1, data3:1, data4:1}, function(err, data_catch,callback) {
if( err || !data_catch ) {
console.log("Problem finding data_catch:" + err);
} else {
data_catch.forEach( function(data_catch_finder,callback) {
data1_db = data_catch_finder.data1;
data2_db = data_catch_finder.data2;
data3_db = data_catch_finder.data3;
data4_db = data_catch_finder.data4;
if(data1_db == "" || data2_db == "" || data3_db == "" || data4_db == ""){error = 1; console.log("Error: data_catch_finder");}
callback(data1_db, data2_db, data3_db, data4_db, error);
});
}
});
callback(data1, data2, data3, data4, error);
}
//########################################################################
start_query(function() {
function start_query2(callback) {
console.log("DATA1 from callback:" + data1_db);
console.log("DATA2 from callback:" + data2_db);
console.log("DATA3 from callback:" + data3_db);
console.log("DATA4 from callback:" + data4_db);
var var_no_db = "testing";
//do something else and callback
callback(var_no_db);
}
start_query2(function() {
console.log("Var from callback start_query2:" + var_no_db);
console.log("The end");
});
});
your callback signature are issuing callback as a parameter.
As far as I can understand your code, you need to keep reference of the first callback, the one you receive here: function start_query(callback).
In every callback function you made the mistake to bind the variable name callback to the parameter from the mongo driver (a simple undefined i think).
You can fix it removing every reference of callback from the signature of your inner functions.
a simple example:
function async (cb) {
// params: Error, data
cb(null, 'moo');
}
function foo(callback) {
async(function(err, data, callback){
console.log(callback); // undefined
});
console.log(callback); // Moo
}
foo('Moo');
Take a look at Eloquent Javascript to better understand the JS context switching;
edit
The only way to wait the results of an async function is recall the first callback inside the last nested callback.
function ugly_nested (callback) {
dbquery('...', function(err, data_01) {
if (!! err) return callback(err);
dbquery('...', function(err, data_02) {
if (!! err) return callback(err);
dbquery('...', function(err, data_03) {
if (!! err) return callback(err);
callback(null, data_01, data_02, data_03);
});
});
});
}
ugly_nested(function(err, data01, data02, data03) {
if (!! err) throw err;
manage_data(data01, data02, data03);
});
The FOR loop is synchronous, but, the database calls are asynchronous, so, the for loop will end before the database returns his results. If you really need that for loop you can try out one of the nice flow control libraries out there
Check below algorithm...
users = getAllUsers();
for(i=0;i<users.length;i++)
{
contacts = getContactsOfUser(users[i].userId);
contactslength = contacts.length;
for(j=o;j<contactsLength;j++)
{
phones = getPhonesOfContacts(contacts[j].contactId);
contacts[j].phones = phones;
}
users[i].contacts = contacts;
}
return users;
I want to develop such same logic using node.js.
I have tried using async with foreach and concat and foreachseries functions. But all fail in the second level.
While pointer is getting contacts of one user, a value of i increases and the process is getting started for next users.
It is not waiting for the process of getting contacts & phones to complete for one user. and only after that starting the next user. I want to achieve this.
Actually, I want to get the users to object with proper
Means all the sequences are getting ruined, can anyone give me general idea how can I achieve such a series process. I am open to change my algorithm also.
In node.js you need to use asynchronous way. Your code should look something like:
var processUsesrs = function(callback) {
getAllUsers(function(err, users) {
async.forEach(users, function(user, callback) {
getContactsOfUser(users.userId, function(err, contacts) {
async.forEach(contacts, function(contact, callback) {
getPhonesOfContacts(contacts.contactId, function(err, phones) {
contact.phones = phones;
callback();
});
}, function(err) {
// All contacts are processed
user.contacts = contacts;
callback();
});
});
}, function(err) {
// All users are processed
// Here the finished result
callback(undefined, users);
});
});
};
processUsers(function(err, users) {
// users here
});
You could try this method without using async:
function getAllUserContacts(users, callback){
var index = 0;
var results = [];
var getUserContacts = function(){
getContactsOfUser(users[index].userId, function(contacts){
var index2 = 0;
var getContactsPhones = function(){
getPhonesOfContacts(contacts[index2].contactId, function(phones){
contacts[index2].phones = phones;
if(index2 === (contacts.length - 1)){
users[index].contacts = contacts;
if(index === (users.length - 1)){
callback(users)
} else {
index++;
getUserContacts();
}
}else{
index2++;
getContactsPhones();
}
});
}
getContactsPhones();
});
}
getUserContacts();
}
//calling the function
getAllUsers(function(users){
getAllUsersWithTheirContacts(users, function(usersWithContacts){
console.log(usersWithContacts);
})
})
//Asynchronous nested loop
async.eachSeries(allContact,function(item, cb){
async.eachSeries(item,function(secondItem,secondCb){
console.log(secondItem);
return secondCb();
}
return cb();
},function(){
console.log('after all process message');
});