I had this function:
exports.profileImage = function(req, res) {
var id = req.params.user_id;
userProvider.get(id, function(err, user){
if (err) throw err;
userProvider.getImageById(user['image_id'], function(err, image) {
if (err) throw err;
userProvider.writeImageToDisk(image, function(err, path){
if (err) throw err;
res.sendfile(path);
});
});
});
};
I rewrite it using local variables:
exports.profileImage = function(req, res) {
var id = req.params.user_id;
var userTemp = undefined;
var imageTemp = undefined;
async.series([
userProvider.get(id, function(err, user){
if (err) throw err;
userTemp = user;
}),
userProvider.getImageById(userTemp['image_id'], function(err, image) {
if (err) throw err;
imageTemp = image;
}),
userProvider.writeImageToDisk(imageTemp, function(err, path){
if (err) throw err;
res.sendfile(path);
})
]);}
I have a parameters which userProvider.getImageById (user json object) needs , it comes from userProvider.get function, Which invoked before, I save it to local variable.
I chose async to skip callback hell but it is not working.
Error:
Cannot read property 'image_id' of undefined.
userTemp is undefined at the point where you try to look up its image_id. It will only become not undefined when the previous asynchronous function has been called.
Using async.waterfall, you should be able to simplify your code considerably to something like (the untested);
var id = req.params.user_id;
async.waterfall([
function(callback) {
userProvider.get(id, callback);
},
function(user, callback) {
userProvider.getImageById(user['image_id'], callback);
},
userProvider.writeImageToDisk,
res.sendfile
]);
That's not how async.series works.
Each function in the array has to have the following signature:
function(callback) { ...; callback(...); };
Once the code for each function is done, you need to call the callback function to signal to async that it should run the next step (docs).
So your code should look like this:
async.series([
function(callback) {
userProvider.get(id, function(err, user) {
if (err) throw err;
userTemp = user;
callback();
});
},
function(callback) {
userProvider.getImageById(userTemp['image_id'], function(err, image) {
if (err) throw err;
imageTemp = image;
callback();
});
},
function(callback) {
userProvider.writeImageToDisk(imageTemp, function(err, path){
if (err) throw err;
res.sendfile(path);
callback();
});
}
]);
Better yet, take a look at async.waterfall for a way of passing results from one async function to the next.
Related
Im trying to connect to my Mongodb and insert some documents if they are not already in the db. It works fine with the first inserts but in the function existInDatabase it sometimes does not execute the callback function.
var MongoClient = require('mongodb').MongoClient;
var mongoData = require('./mongoData');
var exports = module.exports = {};
var dbName = 'checklist';
MongoClient.connect(mongoData.ConString, {
useNewUrlParser: true
}, function(err, db) {
if (err) throw err;
for (var key in mongoData.Customers) {
if (!existsInDatabase(mongoData.Customers[key], 'Customers')) {
db.db(dbName).collection('Customers').insertOne(mongoData.Customers[key], function(err, res) {
if (err) throw err;
console.log('1 document inserted');
db.close();
});
}
}
for (var key in mongoData.Categorys) {
if (!existsInDatabase(mongoData.Customers[key], 'Customers')) {
db.db(dbName).collection('Categorys').insertOne(mongoData.Categorys[key], function(err, res) {
if (err) throw err;
console.log('1 document inserted');
db.close();
});
}
}
});
function existsInDatabase(obj, collection) {
var result = false;
MongoClient.connect(mongoData.ConString, {
useNewUrlParser: true
}, function(err, db) {
db.db(dbName).collection(collection).find({}).forEach(function(doc) {
if (doc.id == obj.id) {
result = true;
}
}, function(err) {
console.log(err);
});
});
return result;
}
I have made a few changes to your code. It seems you are new to async programming, spend some time to understand the flow. Feel free for any further query. Here is your code.
// Welcome to aync programming
// Here no one waits for the slow processes
var MongoClient = require('mongodb').MongoClient;
var mongoData = require('./mongoData');
var exports = module.exports = {};
var dbName = 'checklist';
// Make the connection for once only
MongoClient.connect(mongoData.ConString, { useNewUrlParser: true },
function(err, db) {
if (err) throw err;
var myDB = db.db(dbName); // create DB for once
for (var key in mongoData.Customers) {
//make call to the function and wait for the response
existsInDatabase(mongoData.Customers[key], 'Customers', function(err, result) {
//once the response came excute the next step
if (result) {
myDB.collection('Customers').insertOne(mongoData.Customers[key], function(err, res) {
if (err) throw err;
console.log('1 document inserted');
});
}
});
}
for (var key in mongoData.Categorys) {
//make call to the function and wait for the response
existsInDatabase(mongoData.Customers[key], 'Customers', function(err, result) {
//once the response came excute the next step
if (result) {
myDB.collection('Categorys').insertOne(mongoData.Categorys[key], function(err, res) {
if (err) throw err;
console.log('1 document inserted');
});
}
});
}
// Both the for loop will work randomly without any order
function existsInDatabase(obj, collection, cb) {
var result = false;
myDB.collection(collection).findOne({ id: obj.id }, function(err, result)
{
if (err) {
//this cb will work only when db operation is complited
cb(err);
} else if (result) {
cb(null, true);
} else {
cb(null, false);
}
});
}
});
This code may result in some error. Feel free to ask more questions over it
db.db(dbName).collection(collection).find({}) returns a cursor per the docs. You are missing .toArray():
db.db(dbName).collection(collection).find({}).toArray()...
How to load all of the documents within a database right after a new document has been added to the database?
app.get('/ajax', function(req, res) {
var itemOne = new Todo({item: req.query.item}).save(function(err,data){
if (err) throw err;
});
Todo.find({}, function(err1, data1){
if (err1) throw err;
res.send(data1);
});
});
app.get('/ajax', function(req, res) {
var itemOne = new Todo({item: req.query.item}).save(function(err,data){
if (err) throw err; //Find Records right here
Todo.find({}, function(err1, data1){
if (err1) throw err;
res.send(data1);
});
});});
In your code "save" function and "find" function will run asynchronously so finding inside the callback function will get u all the results
I want to repeat some items in my template (twig) on different places, where each repeated item responds to file names in different directories, so first I need an array with filenames.
I don't know how to affect outer scope from function. This will not work:
var files_list = {'json': [], 'js': []}
fs.readdir('./public/json', function(err, items) {
if (err) throw err;
files_list.json = items;
});
res.render('index', { js: files_list.js, jsons: files_list.json });
This works, but how to render it again to get something from another directory.
fs.readdir('./public/json', function(err, items) {
if (err) throw err;
res.render('index', { jsons: items });
});
This is a var that you does't have synchronously at hand; So you should treat it the asynchronous way:
Use a callback function:
var getFiles = function(dir, cb) {
fs.readdir(dir, function(err, files) {
if (err) cb(err, null);
cb(null, files);
});
};
Usage:
getFiles('./public/json', function(err, files) {
if (err) throw err;
res.render('index', { jsons: files });
});
Or a promise:
var getFiles = function(dir) {
return new Promise(function(resolve, reject) {
fs.readdir(dir, function(err, files) {
if (err) reject(err);
resolve(files);
});
});
};
Usage:
getFiles('./public/json')
.then(function(files) {
res.render('index', { jsons: files });
}, function(err) {
throw err;
});
I would like to get the whole document instead of the added item when I do a save().
var newTodo = Todos({
ID: req.body.ID,
RuleName: req.body.RuleName
});
newTodo.save(function (err, todos) {
if (err) throw err;
res.send(todos);
});
You cannot get it, unless you extend model method, or get it inside save
Simple version
newTodo.save(function (err, todos) {
if (err) throw err;
Todos.find(err, todos) {
if (err) throw err;
res.send(todos);
}
});
Version with custom method
// in schema definition
TodosSchema.methods.saveAndFind = function(cb) {
var self = this;
self.save(function(err) {
if(err) throw err;
return self.model('Todos').find({}, cb);
})
};
// in controller
var newTodo = Todos({
ID: req.body.ID,
RuleName: req.body.RuleName
});
newTodo.saveAndFind(function (err, todos) {
if (err) throw err;
res.send(todos);
});
I have an array of userIDs (MongoDB Objectids)which I want to iterate through and for each one, find its user entry in my MongoDB database of users, and update it, say modify the user's age. Then only when every user has been updated, do I want to say res.send(200); in my Node.js Express app.
I started out with the following code which is just plain wrong because of the asynchronous calls to findById:
for (var i = 0; i < userIDs.length; i++) {
var userID = userIDs[i];
User.findById(userID, function (err, user) {
if (err) throw err;
// Update user object here
user.save(function (err, user) {
if (err) throw err;
res.send(200);
});
});
}
Any ideas how I can do this? Is there perhaps a synchronous version of findById? Or perhaps a way to map through the array and apply a function to each element?
Thanks!
I think you want the forEach method of npm's async module. It would look something like this:
async.forEach(userIDs, function(id, callback) {
User.findById(id, function(err, user){
if(err) throw err;
user.save(function(err, user){
if(err) throw err;
callback();
}
}, function(err){
if(err){
throw err;
} else {
res.send(200);
}
}
}
The best way is to use promises.
An example with Q#all:
var q = require('Q');
var promises = userIDs.map(function(userID){
var deferred = q.defer();
User.findById(userID, function (err, user) {
if (err) return deferred.reject(err);
// Update user object here
user.save(function (err, user) {
if (err) return deferred.reject(err);
deferred.resolve(user);
});
});
return deferred.promise;
});
q.all(promises)
.then(function(users){
res.json(users);
})
.fail(function(err){
res.send(500,err);
});