How to insert data to mongo synchronously (Nodejs, Express)

问题

I have a problem with inserting data to mongo db using node(express)

My code looks like this:

router.get('/data/:section/:sort', function(req, res, next) {
//Deleting old data always before writing new
//Image.remove().exec();
var section = req.params.section;
var sort = req.params.sort;
//Link to Igmur API
var url = 'https://api.imgur.com/3/gallery/'+section+'/'+sort+'/1'; //1 at the end is used to get more than 60 images(gives only 60 without it)
    request.get({
    url: url,
    method: 'GET',
    headers: {
        'Authorization': 'Client-Id XXXXXXXXXXXXX'
    }}, function(e, r, body){
var metadata = JSON.parse(body);
for(var i = 0; i<100; i++){
        var image = new Image(metadata.data[i])
        image.save(function(err, result){
        });
};res.render('index', { title: 'SearchAPI' });});});

The problem is that I get only about 20 objects inserted instead of 100 as u can see in the loop. All because node just jump forward before the save method is completely done. How can I fix this? Thank you in advance

回答1:

Use a promise library such as Q

What you basically need to do is wait for all your save methods to complete. Use the Q.all method which waits for everything to be executed.

var Q = require('q');

var promiseArr = [];

for(var i = 0; i<100; i++){
        var imgDefer = Q.defer();
        var image = new Image(metadata.data[i])
        image.save(function(err, result){
             if(err)imgDefer.reject(err);
             else imgDefer.resolve()
        });
       promiseArr.push(imgDefer);
}
Q.all(promiseArr).then (function (){
    res.render('index', { title: 'SearchAPI' });
})

回答2:

Calling the database again and again is a wrong practice it's better if you use create and pass everything at once. Have a look at the snippet below. Hope it helps.

router.get('/data/:section/:sort', function(req, res, next) {
  //Deleting old data always before writing new
  //Image.remove().exec();
  var section = req.params.section;
  var sort = req.params.sort;
  //Link to Igmur API
  var url = 'https://api.imgur.com/3/gallery/'+section+'/'+sort+'/1'; //1 at the end is used to get more than 60 images(gives only 60 without it)
  request.get({
    url: url,
    method: 'GET',
    headers: {
    'Authorization': 'Client-Id XXXXXXXXXXXXX'
  }}, function(e, r, body){
    var metadata = JSON.parse(body);

    Image.create(metadata.data,(err, result)=>{
      //do operations here
      res.render('index', { title: 'SearchAPI' });
    })

    /* WRONG PRACTICE */
    // for(var i = 0; i<100; i++){
    //   var image = new Image(metadata.data[i])
    //   image.save(function(err, result){

    //   });
    // };

  });
});

来源：https://stackoverflow.com/questions/40191639/how-to-insert-data-to-mongo-synchronously-nodejs-express

标签

node.js

mongodb

express

asynchronous

synchronous