I am new to sequelize and NodeJS promises in general. My app basically saves tweets from the Twitter API, but also needs to update some of the saved tweets' data in realtime, like the Retweet count or the Liked count.
But it seems like after fetching the new data, when trying to run all the update on my tweet instances, nothing happens. The promise doesn't go through.
To sum up : I find 100 saved tweets, chain on a callback that fetches their new data from Twitter, and then chain on updating every single 100 tweets with the new data. The later update doesn't go through.
var Sequelize = require('sequelize');
...
//Getting 100 tweets previously saved in DB
Sequelize.query("SELECT * FROM tweets WHERE ORDER BY id DESC LIMIT 100", { model: Model }).then(function(result) {
if(result.length == 0) {
callback(false);
} else {
var ids = [];
var realData = {};
for (var i in result) {
realData[result[i].dataValues.id_str] = result[i];
ids.push(result[i].dataValues.id_str);
}
//getting twitter data for 100 tweets previously saved in DB
twitVendor.get('statuses/lookup', {
id : ids.join(',')
}, function (err, tweets, response) {
if (typeof err == 'undefined') {
//to get a synchronous saving of all tweets
//this could be cleaned up with a Sequelize.Promise.push(...)
var i = 0;
var saving = false;
while (i < tweets.length) {
if (!saving) {
saving = true;
console.log('Updating tweet ', tweets[i].id_str);
//updating tweet with new data from twitter
Sequelize.query("UPDATE tweets SET retweet_count = "+tweets[i].retweet_count+", favorite_count = "+tweets[i].favorite_count+" WHERE id_str = '"+tweets[i].id_str+"'", {
model: Model
}).then(function(result) {
console.log('Updated tweet');
saving = false;
i++;
}).catch(function (err) {
console.log('Failed to update post ', err);
saving = false;
i++;
});
}
}
callback(true);
console.log("Updated tweets");
} else {
console.log("Failed :", err);
callback(false, err);
}
});
}
}).catch(function (err) {
console.log("Failed :", err);
callback(false, err);
})
EDIT : If you want to execute the above code, I'd recommend using this Twit to hit the Twitter API : https://github.com/ttezel/twit
To get credentials to hit the API, you will need to set up an app on Twitter though : https://apps.twitter.com/
EDIT 2 : I already tried to use transactions and pure Sequelize functions to make my queries, but the issue stood still.
Don't nest promises inside of promises. Instead, chain them by returning promises. If you are returning something that is not a promise, use Promise.resolve(value) to turn it into a promise. And certainly don't put promises inside of callbacks, or even mix them at all; instead create a promise that calls the action, and then in the callback resolve the promise.
Here's my attempt to rewrite what you're trying to do. You may need to wrap the first in a Promise.resolve to take advantage of returning the new promise:
Sequelize.query("SELECT * FROM tweets WHERE ORDER BY id DESC LIMIT 100"
, { model: Model }).then(function (results) {
if (results.length == 0) {
return Promise.reject(false); //reject to hit the catch of the promise. Change false to error.
}
var ids = [];
var realData = {};
for (var i in result) {
realData[result[i].dataValues.id_str] = result[i];
ids.push(result[i].dataValues.id_str);
}
return new Promise((resolve, reject) => {
twitVendor.get('status/lookup', {
id: ids.join(',')
}, function (err, tweets, response) {
if (err) {
reject(false); //reject to hit the catch of the promise. Change false to error message
}
resolve(tweets);
})
})
}).then(function (tweets) {
function updateTweet(tweet) {
return sequelize.query(...);
}
var updatesInParallel = tweets.map(updateTweet);
return Promise.all([updatesInParallel]);
}).then(function () {
callback(true);
}).catch(function (error) {
console.log("failed: ", error);
callback(false)
});
Related
I have created Node JS app, i am explicitly downloading more than 100000 records from database. While the request is in proceeding, i try to login in the same application from another browser it wont respond unless the previous request is completed. Any idea ? Anything to do with event loop or threads ??
So here is my logic.
I make a get request to my API in Step 1, API calls database layer in Step 2. Database is returning only 21 records, i am explicitly looping 100000*21 to make heavy rendering just to test the load on json2csv. While doing so, the other requests to server will not respond until the last processing completes.
Step 1:
router.get('/report/downloadOverdueTrainings/:criteria', function (req, res, next) {
var overDueTrainings = [];
var reportManager = new ReportManager();
var result = reportManager.getOverdueTrainings(JSON.parse(req.params.criteria));
result.then(function (result) {
var fields = ['Over Due Trainings'];
for (var i = 0; i < 100000; i++) { //Testing purpose
for (var training of result) {
overDueTrainings.push({
'Over Due Trainings': training.OverDueTrainings
})
}
}
json2csv({
data: overDueTrainings,
fields: fields
}, function (err, csv) {
if (err)
throw err;
res.setHeader('Content-disposition', 'attachment; filename=OverdueTrainings.csv');
res.set('Content-Type', 'text/csv');
res.send(csv);
});
}).catch(function (err) {
next(err);
});
});
Step 2: Database Logic
var xtrDatabaseConnection =require('./xtrDatabaseConnection').XTRDatabaseConnection;
ReportData.prototype.getOverdueTrainings = async function (params) {
var connection = new xtrDatabaseConnection();
var sequelize = connection.getSequelize();
try {
var query = "CALL report_getOverdueTrainings(:p_CourseCode,:p_Revision,:p_RevisionNo,:p_UserGroup,:p_Username,:p_Status,:p_SortColoumnNo,:p_SortColoumnDirection,:p_callType,:p_StartIndex,:p_PageSize)";
var replacements = {
p_CourseCode: params.CourseCode,
p_Revision: params.Revision,
p_RevisionNo: (params.RevisionNo == '' || params.RevisionNo == null) ? 0 : params.RevisionNo,
p_UserGroup: params.UserGroup,
p_Username: params.Username,
p_Status: params.Status,
p_SortColoumnNo: params.SortColoumnNo,
p_SortColoumnDirection: params.SortColoumnDirection,
p_callType: params.callType,
p_StartIndex: params.startIndex,
p_PageSize: params.pageSize
};
//console.log(replacements);
return await connection.executeQuerySequelize(sequelize, query, Sequelize.QueryTypes.RAW, replacements);
} catch (e) {
throw (e);
} finally {
//To close connections
sequelize.connectionManager.close().then(() => console.log('Connection Closed'));
}
}
XTRDatabaseConnection.prototype.executeQuerySequelize = function (sequelize, query, queryType, replacements) {
return sequelize.authenticate()
.then(() => {
return sequelize.query(query, {
replacements: replacements,
type: queryType
}).
then(result => result)
.catch(err => {
throw (err);
});
})
.catch(err => {
xtrUtility.logErrorsToWinstonTransports('Unable to connect to the database or some error occurred while executing your query. ', err);
throw new AppError(err, "dbError", "Unable to connect to the database or some error occurred while executing your query.");
});
}
NodeJS is single-thread, single process. As long as a javascript function is running, nothing else can run. This is by design. The event loop will only kick in again once your functions have stopped executing.
This is blocking:
for (var i = 0; i < 100000; i++) { //Testing purpose
for (var training of result) {
overDueTrainings.push({
'Over Due Trainings': training.OverDueTrainings
})
}
}
until the execution is finished.
also
var result = reportManager.getOverdueTrainings(JSON.parse(req.params.criteria));
result.then(function (result) {
/****/
return await connection.executeQuerySequelize(sequelize, query, Sequelize.QueryTypes.RAW, replacements);
Node.js is working on single thread. So you need use it for small process with async calls. When you use async/await you are blocking the callback function.
So you need to use your database functions as promise. It will work async.
.query('CALL someFunction()')
.then(function(response){
//done
}).error(function(err){
//error
});
But there is a problem about it. You need to load 21 times your result. So in this case you need to use recursive function. When you finished recursive call you can send your data to client as async.
The concept of promises is very new for me (so far, I was working with async.each and async.waterfall)
I want to use promises but i'm stuck right now.
I want to get "tags" from my db.
I have two tables for this : One called 'tags' with every tag in it (with an ID) and another one 'user_tags' with every username saved and the ID of the tag that the user (username) created and saved into 'tags'.
I can put information in my DB but now I want to pull this out and log it out (I will display it later)
So far this is my idea :
var getUserprofile = function getUserprofile(username, callback){
pool.getConnection(function (err, connection) {
var dataUser = [];
// Error check
if (err) {
console.log(err);
}
connection.query('SELECT * FROM users_tags FULL JOIN tags ON (tags.id = users_tags.t_id) WHERE users_tags.user_id=666;', username , function (err, rows, fields) {
if (err) {
connection.release();
cb(err);
} else if (rows.length < 1) {
connection.release();
cb("We don't have any informations about this user yet");
} else {
console.log("we pull the information right now");
connection.release();
callback(null, rows[0]);
}
});
});
}
Is this a good idea ? What should I do if I want to use promises for this kind of function ?
Thanks in advance for any help !!!
I would use Bluebird. You can "promisify" existing APIs with Promise.promisify or Promise.promisifyAll.
I would do something like
var Promise = require('bluebird'),
... //other deps;
var pool = Promise.promisifyAll(pool);
function getUserprofile(username){
var connection = null;
return pool.getConnectionAsync()
.then(function (conn) {
connection = Promise.promisifyAll(conn);
return connection.queryAsync('...');
})
.then(function (results) {
if (results.length < 1) {
return "We don't have any informations about this user yet";
} else {
console.log("we pull the information right now");
return results[0];
}
})
.catch(function (err) {
console.log(err);
throw err;
})
.finally(function () {
if (connection) {
connection.release();
}
});
}
I am trying to build a login API using NodeJS, but my code is not doing what I expect it to. I am very new to js, promises and all so please simplify any answer if possible.
From what I can see in the output of my code, the first promise part does not wait until the function findUsers(...) is finished.
I have a routes file where I want to run a few functions sequentially:
Find if user exist in database
if(1 is true) Hash and salt the inputted password
... etc
The routes file now contains:
var loginM = require('../models/login');
var loginC = require('../controllers/login');
var Promise = require('promise');
module.exports = function(app) {
app.post('/login/', function(req, res, next) {
var promise = new Promise(function (resolve, reject) {
var rows = loginM.findUser(req.body, res);
if (rows.length > 0) {
console.log("Success");
resolve(rows);
} else {
console.log("Failed");
reject(reason);
}
});
promise.then(function(data) {
return new Promise(function (resolve, reject) {
loginC.doSomething(data);
if (success) {
console.log("Success 2");
resolve(data);
} else {
console.log("Failed 2");
reject(reason);
}
});
}, function (reason) {
console.log("error handler second");
});
});
}
And the findUser function contains pooling and a query and is in a models file:
var connection = require('../dbConnection');
var loginC = require('../controllers/login');
function Login() {
var me = this;
var pool = connection.getPool();
me.findUser = function(params, res) {
var username = params.username;
pool.getConnection(function (err, connection) {
console.log("Connection ");
if (err) {
console.log("ERROR 1 ");
res.send({"code": 100, "status": "Error in connection database"});
return;
}
connection.query('select Id, Name, Password from Users ' +
'where Users.Name = ?', [username], function (err, rows) {
connection.release();
if (!err) {
return rows;
} else {
return false;
}
});
//connection.on('error', function (err) {
// res.send({"code": 100, "status": "Error in connection database"});
// return;
//});
});
}
}
module.exports = new Login();
The output i get is:
Server listening on port 3000
Something is happening
error handler second
Connection
So what I want to know about this code is twofold:
Why is the first promise not waiting for findUser to return before proceeding with the if/else and what do I need to change for this to happen?
Why is error handler second outputed but not Failed?
I feel like there is something I am totally misunderstanding about promises.
I am grateful for any answer. Thanks.
Issues with the code
Ok, there are a lot of issues here so first things first.
connection.query('...', function (err, rows) {
connection.release();
if (!err) {
return rows;
} else {
return false;
}
});
This will not work because you are returning data to the caller, which is the database query that calls your callback with err and rows and doesn't care about the return value of your callback.
What you need to do is to call some other function or method when you have the rows or when you don't.
You are calling:
var rows = loginM.findUser(req.body, res);
and you expect to get the rows there, but you won't. What you'll get is undefined and you'll get it quicker than the database query is even started. It works like this:
me.findUser = function(params, res) {
// (1) you save the username in a variable
var username = params.username;
// (2) you pass a function to getConnection method
pool.getConnection(function (err, connection) {
console.log("Connection ");
if (err) {
console.log("ERROR 1 ");
res.send({"code": 100, "status": "Error in connection database"});
return;
}
connection.query('select Id, Name, Password from Users ' +
'where Users.Name = ?', [username], function (err, rows) {
connection.release();
if (!err) {
return rows;
} else {
return false;
}
});
//connection.on('error', function (err) {
// res.send({"code": 100, "status": "Error in connection database"});
// return;
//});
});
// (3) you end a function and implicitly return undefined
}
The pool.getConnection method returns immediately after you pass a function, before the connection to the database is even made. Then, after some time, that function that you passed to that method may get called, but it will be long after you already returned undefined to the code that wanted a value in:
var rows = loginM.findUser(req.body, res);
Instead of returning values from callbacks you need to call some other functions or methods from them (like some callbacks that you need to call, or a method to resolve a promise).
Returning a value is a synchronous concept and will not work for asynchronous code.
How promises should be used
Now, if your function returned a promise:
me.findUser = function(params, res) {
var username = params.username;
return new Promise(function (res, rej) {
pool.getConnection(function (err, connection) {
console.log("Connection ");
if (err) {
rej('db error');
} else {
connection.query('...', [username], function (err, rows) {
connection.release();
if (!err) {
res(rows);
} else {
rej('other error');
}
});
});
});
}
then you'll be able to use it in some other part of your code in a way like this:
app.post('/login/', function(req, res, next) {
var promise = new Promise(function (resolve, reject) {
// rows is a promise now:
var rows = loginM.findUser(req.body, res);
rows.then(function (rowsValue) {
console.log("Success");
resolve(rowsValue);
}).catch(function (err) {
console.log("Failed");
reject(err);
});
});
// ...
Explanation
In summary, if you are running an asynchronous operation - like a database query - then you can't have the value immediately like this:
var value = query();
because the server would need to block waiting for the database before it could execute the assignment - and this is what happens in every language with synchronous, blocking I/O (that's why you need to have threads in those languages so that other things can be done while that thread is blocked).
In Node you can either use a callback function that you pass to the asynchronous function to get called when it has data:
query(function (error, data) {
if (error) {
// we have error
} else {
// we have data
}
});
otherCode();
Or you can get a promise:
var promise = query();
promise.then(function (data) {
// we have data
}).catch(function (error) {
// we have error
});
otherCode();
But in both cases otherCode() will be run immediately after registering your callback or promise handlers, before the query has any data - that is no blocking has to be done.
Summary
The whole idea is that in an asynchronous, non-blocking, single-threaded environment like Node.JS you never do more than one thing at a time - but you can wait for a lot of things. But you don't just wait for something and do nothing while you're waiting, you schedule other things, wait for more things, and eventually you get called back when it's ready.
Actually I wrote a short story on Medium to illustrate that concept: Nonblacking I/O on the planet Asynchronia256/16 - A short story loosely based on uncertain facts.
So i'm having an issue with handling async actions in NodeJS while trying to send response to a request, with some async calls in the middle. (And to make this party even more complicated, i'm also want to use async.parallel )
Basically i'm trying to get value from Redis, and if he doesn't exist, get it from a provider (with request and response based using axios).
This is the code snippet :
this.getFixturesByTimeFrame = function (timeFrame, res) {
function getGamesData(timeFrame,finalCallback) {
var calls = [];
var readyList = [];
//Creating calls for parallel
timeFrame.forEach(function(startDay){
calls.push(function(callback) {
//Problematic async call
redisClient.get(startDay, function (error, exist) {
console.log('Got into the redis get!');
if (error){
console.log('Redis error : '+error);
}
if (exist) {
console.log('Date is in the cache! return it');
return exist;
} else {
//We need to fetch the data from the provider
console.log('Date is not in the cache, get it from the provider');
getFixturesDataFromProvider(startDay)
.then(organizeByLeagues)
.then(function (gamesForADay) {
redisClient.setex(startDay, 600, gamesForADay);
responsesList.add(gamesForADay);
callback(null, gamesForADay);
}).catch(function (response) {
if (response.status == 404) {
callback('Cant get games from provider');
}
});
}
});
}
)});
async.parallel(calls, function(err, responsesList) {
/* this code will run after all calls finished the job or
when any of the calls passes an error */
if (err){
res.send(501);
} else {
console.log('Here is the final call, return the list here');
//Some data manipulation here - just some list ordering and for each loops
console.log('finished listing, send the list');
finalCallback(responsesList);
}
});
}
getGamesData(timeFrame, function (readyList) {
res.send(readyList);
});
};
function getFixturesDataFromProvider(date) {
var requestUrl = 'someURL/ + date;
return axios.get(requestUrl, config);
}
function organizeByLeagues(matchDay) {
if (matchDay.count == 0) {
console.log('No games in this day from the provider');
return [];
} else {
var organizedSet = [];
//Some list manipulations using for each
return organizedSet;
}
}
But the response is been sent before parallel has been starting doing his things...
i'm missing something with the callbacks and the async calls for sure but i'm not sure where...
Thanks
I'm using a function which returns data in a paginated form. So it'll return max 100 items and a key to retrieve the next 100 items. I want to retrieve all the items available.
How do I recursively achieve this? Is recursion a good choice here? Can I do it any other way without recursion?
I'm using Bluebird 3x as the promises library.
Here is a snippet of what I'm trying to achieve:
getEndpoints(null, platformApplication)
.then(function(allEndpoints) {
// process on allEndpoints
});
function getEndpoints(nextToken, platformApplication) {
var params = {
PlatformApplicationArn: platformApplication
};
if (nextToken) {
params.NextToken = nextToken;
}
return sns.listEndpointsByPlatformApplicationAsync(params)
.then(function(data) {
if (data.NextToken) {
// There is more data available that I want to retrieve.
// But the problem here is that getEndpoints return a promise
// and not the array. How do I chain this here so that
// in the end I get an array of all the endpoints concatenated.
var moreEndpoints = getEndpoints(data.NextToken, platformApplication);
moreEndpoints.push.apply(data.Endpoints, moreEndpoints);
}
return data.Endpoints;
});
}
But the problem is that if there is more data to be retrieved (see if (data.NextToken) { ... }), how do I chain the promises up so that in the end I get the list of all endpoints etc.
Recursion is probably the easiest way to get all the endpoints.
function getAllEndpoints(platformApplication) {
return getEndpoints(null, platformApplication);
}
function getEndpoints(nextToken, platformApplication, endpoints = []) {
var params = {
PlatformApplicationArn: platformApplication
};
if (nextToken) {
params.NextToken = nextToken;
}
return sns.listEndpointsByPlatformApplicationAsync(params)
.then(function(data) {
endpoints.push.apply(endpoints, data.Endpoints);
if (data.NextToken) {
return getEndpoints(data.NextToken, platformApplication, endpoints);
} else {
return endpoints;
}
});
}
For a more general purpose example of recursively getting and returning data from a paginated endpoint, here is what I came up with:
getData(page, dataArray) {
return new Promise((resolve, reject) => {
getEndpointHere(
{
page,
pageSize: 50,
},
(err, result) => {
if (err)
return console.error("there was a problem retrieving your data");
dataArray = dataArray.concat(result);
if (result.length < 50) {
resolve(dataArray);
} else {
resolve(getData(page + 1, dataArray));
}
}
);
});
}
getData(1, [])
.then((res) => {
console.log("SEVERAL PAGES OF DATA", res);
})
This example is employing a callback -- (err, result) -- however, that logic could be extracted out to handle the response from the endpoint. The resource I was consuming does not return a cursor or "next" token indicating if there are more records, so I used the logic of if the response has less than 50 records as the basis for continuing to request more data.