recursive find function calls then merge result

Question

recursive find function calls then merge result

i cant merge the result of each FIND functions in this code :

this.result = [];
    _products.find().exec(function (err,products) {
        this.products = products;
        var productsCollection = [];
        for(i=0;i<products.length;i++) {
            _prices.find({uname:products[i].uname},function(err,prices){

                var resultItem = {product:products[i],prices:prices}
                this.result.push(resultItem)
            }.bind(this))

        }
            res.json(200, this.result);
    }.bind(this) );

there is no error ... but the response is an empty array :(

please help ... how can i merge results ?

javascript
node.js
mongodb
mongoose

Answer 1

You're calling res.json before you've recieved the result of _prices.find({uname..., since .find is asynchronous. The simple solution is to use async to loop through the array and call res.json when all results are recieved.

var async = require('async');
this.result = [];

_products.find().exec(function (err, products) {
    // async.map takes an array and constructs a new array from it
    // async.each and this.result.push() would also work but I find .map to be cleaner
    async.map(products, function (product, next) {
        _prices.find({ uname: product.uname }, function(err, prices){
            // By passing the object to next here it will be passed to the
            // final callback below
            next(err, { product: product, prices: prices });
        });
    }, function (err, result) {
        // This callback will nicely wait until all queries above has finished
        this.result = result;
        res.json(200, result);
    });
}.bind(this));