exports.getCityCascade = function (req, res) {
var result = {};
Province.find().exec(function (err, provinces) {
result.provinces = provinces;
var provinceCount = 0;
async.whilst(
function () {
return provinceCount < provinces.length
}
, function (callback) {
City.find({province: provinces[provinceCount].id}).exec(function (err, cities) {
if (err) {
callback(err);
} else {
result.provinces[provinceCount].cities =cities;
}
provinceCount++;
callback(null , result);
});
}, function (err, result) {
if (err) return res.jsonp({message: err.message});
return res.jsonp({
status: '200',
results: result});
}
)
})
}
When I add the cities field to provinces, It seems doesn't work. the response body doesn't contain the filed cities. How to fix it? Any advice would be very helpful.
The problem is just a conflict between variable names: you declared a var result outside Province.find(), but the async.whilst() also uses result as the second argument of its callback function. Just rename one of them and it should work.
Related
Hello I am having an issue with the following sequence, I need to run multiple queries which build on each other that are in a for loop then once the final result is obtained to implement the result. I am having an issue where my for loop is looping past the query, also I need to stop the code while the findX function is running.
I know this is an async problem but I don't see how I could chain promises, or use the async npm package with needing to loop queries that depend on the result of the previous query. Thanks in advance.
function findX(){
//executes another query
}
function solve(res, connection, info, requestArr, callback){
var parentID = null;
var obj = {};
for (var i = 0; i <= requestArr.length; i++) {
connection.query("SELECT WHERE ", [parentID, requestArr[i]], function(err, results) {
if(results[0]['x']){
var obj = findX(x)
break;
}else{
parentID = results[0]['parentID'];
}
});
}
//Do stuff with obj only after the final result has been set in the for loop
}
You can use Async TimesSeries.
// Pretend this is some complicated async factory
var createUser = function(id, callback) {
callback(null, {
id: 'user' + id
});
};
// generate 5 users
async.times(5, function(n, next) {
createUser(n, function(err, user) {
next(err, user);
});
}, function(err, users) {
// we should now have 5 users
});
So, in your example would be something like this:
var iterations = requestArr.length - 1,
parentID,
obj;
var getResults = function (i, callback) {
connection.query("SELECT WHERE ", [parentID, requestArr[i]], function (err, results) {
if (results[0]['x']) {
obj = findX(x);
callback('done');
}
else {
parentID = results[0]['parentID'];
callback();
}
});
};
async.timesSeries(iterations, function (n, next) {
getResults(n, function (err) {
next(err);
});
}, function (err) {
// use obj
});
I have a question about asynchronous function. Here my function "My_function":
function My_function (my_name, callback){
stmt = db.prepare ("SELECT number_table1 from my_table1 WHERE user=?");
stmt.bind(my_name);
stmt.get(function(error,row){
if(error){
throw err;
}
else{
if(row){
callback(number_table1);
}
else{
console.log("error");
}
}
});
}
Work fine but I have 2 tables and I need do other query and I need add two numbers so... in my function I need do too this query:
stmt = db.prepare ("SELECT number_table2 from my_table2 WHERE user=?");
and finally return back in my callback "number_table1 + number_table2".
Somebody know how to solve it? Thanks in advance.
Best regards!
In cases like your's I like to use the async module, because the code will be more legible. Example:
var async = require('async');
function My_function(my_name, callback) {
var stmt = db.prepare("SELECT number_table1 from my_table1 WHERE user=?");
stmt.bind(my_name);
stmt.get(function (error, row) {
if (error) {
callback(error, null);
} else {
if (row) {
callback(null, number_table1);
} else {
callback(new Error("row not found"), null);
}
}
});
}
//if you need the results in a specific order, you can use "series" instead of "parallel".
async.parallel(
//array of functions
[
function (callback) {
My_function('firstName', callback);
},
function (callback) {
My_function('secondName', callback);
}
],
//results when all functions ends
//the results array will equal [number_table1, number_table2], but the order can be different, because of the parallelism
function (err, results) {
if (err) {
//handle the err
} else {
//do something
}
}
);
Docs:
http://caolan.github.io/async/docs.html#parallel or
http://caolan.github.io/async/docs.html#series
You need to synchronize the functions so that you can be sure both their results are ready before calling back. You can do this using promises: https://www.promisejs.org/
Make two regular functions (no callbacks), one for each query (function1, function2)
Make both return a promise
Then you can do
function My_function(my_name) {
var value1;
function1(my_name)
.then(function(resultFromFunction1) {
value1 = resultFromFunction1;
return function2(my_name);
})
.then(function(resultFromFunction2) {
var result = value1 + resultFromFunction2;
return result;
});
}
}
Make sure to catch errors and handle different outcomes, what I presented is its simplest form.
Update
Here is an example of a function doing a query and returning a promise
function1 = function(user) {
return new Promise(function (resolve, reject) {
pool.getConnection(function (err, connection) {
if(err) {
reject ({status : false, message : "Error in connection database"});
} else {
connection.query('SELECT number_table1 from my_table1 WHERE user=?', [user], function(err, rows){
connection.release();
if(!err) {
resolve ({status: true, message: rows});
} else {
reject ({status: false, message: err});
}
});
}
});
});
}
Make the table names function parameters. Convert that function to use async/await or promise. Use Promise.all to run both queries.
var shortLinks = [];
Link.find({}, function (err, links) {
if (err) {
console.log(err);
} else {
links.map(link => {
shortLinks.push(link.shortLink);
});
}
console.log(shortLinks);//shortLinks has values, all okey
});
console.log(shortLinks); //shortLinks is empty
i need to use shortLinks after Link.find({}) but array is empty.
Need to return shortLinks.
Callbacks. The function(err, links) is called asynchronously, so shortLinks isn't populated until that function is called. Your bottom console.log is being called first, due to how callbacks work.
https://developer.mozilla.org/en-US/docs/Mozilla/js-ctypes/Using_js-ctypes/Declaring_and_Using_Callbacks
need to use promise:
const shortLinks = [];
const getShortLinks = Link.find({}, function (err, links) {
if (err) {
console.log(err);
} else {
links.map(link => {
shortLinks.push(link.shortLink);
});
}
});
getShortLinks.then(function(links){
console.log(shortLinks);
}, function(err){
console.log(err);
});
I am mew to node js, I have something like this,
get_contacts(data, function(contacts) {
if (contacts.length) {
var count = contacts.length;
for (var i = 0; i < count; i++) {
result = {
id: contacts[i].id,
name: contacts[i].name,
sent1: get_sent(data.userId, contacts[i].id, function(resp) {
result.sent = resp.count;
}),
}
result1[i] = result;
}
output = {
contacts: result1,
}
} else {
output = {
error: "No Contacts.",
}
}
res.writeHead(200, {'content-type': 'text/html'});
res.end(JSON.stringify(output));
});
get_contacts is a callback function which will return contact list.result1 & result are objects. Now value for sent should come from a function get_sent, and get sent is like this
function get_sent(userId, contactId, callback) {
pool.getConnection(function(err, connection) {
connection.query("my query here", function(err, rows) {
connection.release();
if (!err) {
callback(rows);
} else {
console.log(err)
}
});
});
}
But im not getting any value since nodejs. since nodejs is async it is not waiting for the function to return value. I know, im doing it in wrong way. Please help
You need to use a callback. In simple words is a function that you'll execute after something happens. You should read more about that. You should get a book about javascript but you can start reading here for example.
About your case, you could solve it like this
//Asumming that you object `result` is global.
result = {
id: contacts[i].id,
name: contacts[i].name,
sent: -1 //Some default value
}
//Just to put the code into a function, you have to put it where you need
function constructObject (){
get_sent(uId, cId, function(err, total){
if(err){
console.log("Something was wrong.", err);
}
result.sent = total;
//Here you have your object completed
console.log(result);
});
}
//You need to use a callback
function get_sent(uId, cId, callback) {
pool.getConnection(function(err, connection) {
//Note that I add an alias here
connection.query("SELECT count(*) as total FROM table_name", function(err, rows) {
connection.release();
if (!err) {
//I am returning the result of the query and a null error
callback(err, rows[0].total);
} else {
console.log(err);
//I am returning an error
callback(err);
}
});
});
}
//For example you could call this function here
constructObject();
And it depends of what are you doing exactly but Maybe you need a callback on your constructObject too.
Hi I have this code but when finish the result is not the espected because didn't run in the sequence that I wish
here is the code:
var user_data = {};
models.games.find({$or: [{w_id: req.user._id}, {b_id: req.user._id}, {owner: req.user._id}]}, function (err, games) {
var req_games = [];
if (!err) {
for (var i in games) {
req_games.push(games[i]);
models.users.findOne({_id: games[i].w_id}, function (err, user) {
req_games[i].w_id = user.user;
console.log(req_games[i].w_id) //< -- 3
});
console.log('a ' + req_games[i].w_id) //<-- 2
}
user_data.games = req_games; // <-- 1
}
});
at the end of the task req_games didnt have any update because it's running in the sequence that I put in the comments in the code
This may help you using Q(promises)
obj.find = function(model, condition) { //make your find to return promise
var deferred = q.defer();
model.find(condition, function(err, results) {
if (err) {
logger.log(err);
deferred.reject(err);
} else {
deferred.resolve(results);
}
});
return deferred.promise;
}
ArraysOfId.forEach(function (id) {
var tempProm = mongoUtilsMethodObj.find(schemaObj.Asset, id).then(function (assetObj) {
---- your code
return q.resolve();
});
promArr.push(tempProm);//push all promise to array
});
q.all(promArr).then(function () {
// this will be called when all promise in array will we resolved
})
Here is a version using the async library to map your game values.
var async = require('async');
var user_data = {};
models.games.find({$or: [{w_id: req.user._id}, {b_id: req.user._id}, {owner: req.user._id}]}, function (err, games) {
if(err) {
// or whatever your error response happens to be
return res.render('user.swig', {error: err});
}
async.map(games, function(game, nextGame) {
models.users.findOne({_id: game.w_id}, function (err, user) {
game.w_id = user.user;
nextGame(err, game);
});
}, function(err, req_games) {
user_data.games = req_games;
res.render('user.swig', {user: user_data});
});
});