Node.Js Async usage

Question

My Process1() function has a database loop, so Process2() and Process3() calling more than once. Which function should I use in async, to wait for a for loop?

 async.waterfall([
 function(callback){
 Process1(yyy, function(){
 //process1 function has a for loop.
 callback();
 })
 },
 function(callback){
 Process2(function(){
 // so process2() is calling more than once
 callback();
 })
 }
], function (callback) {
 Process3()
});

Process1() :

function Process1(yyy, pass){
user.find({}).exec(function(e, users){
 _.each(users, function(_user){
 user.findOneAndUpdate(
 {'_id' : user_id},
 {$inc : {'xxx' : yyy}},
 function(e){
 !e && pass()
 })
 })
})
}

• Brad: It will always wait for a for loop. It has to.
• Lazy: But I have to run that database process before process2. Aren't there any solution? @Brad thanks.
• Brad: That's what will happen with the code you have shown here. Process2 won't run until callback in the first closure is called.
• lwang135: What does your Process1 for loop do? Is it a series of DB calls? If not, then you can put the async to the db process.
• tadman: In my experience this kind of code is easier to express using the promise model, they're a lot easier to chain.

Answer 1

Looking at your code, Process2 will definitely be called more than once, because lodash and underscore does not wait until the call back happens. They are just utilities methods.

To solve asynchronous situations like this, just use async.each or async.eachSeries.

function Process1(yyy, pass){
 user.find({}).exec(function(e, users){
 async.each(users, function(_user, next){
 user.findOneAndUpdate(
 {'_id' : user_id},
 {$inc : {'xxx' : yyy}},
 function(e){
 !e && next()
 })
 }, function(err) {
 pass();
 })
 })
}

• Lazy: Thank you so much, I've understood the async usage thanks to you.