server.js

var express = require('express');
var app = express();
var bodyParser = require('body-parser');
var mongoose = require('mongoose');
var db = mongoose.connect('mongodb://localhost/swag-shop');

var Product = require('./model/product');
var WishList = require('./model/wishlist');

app.use(function (req, res, next) {
  res.header('Access-Control-Allow-Origin', '*'); // * => allow all origins
  res.header('Access-Control-Allow-Methods', 'GET,PUT,POST,OPTIONS,DELETE');
  res.header('Access-Control-Allow-Headers', 'Content-Type, X-Auth-Token, Accept'); // add remove headers according to your needs
  next()
})

app.use(bodyParser.json());
app.use(bodyParser.urlencoded({extended: false}));

app.listen(3002,function(){
    console.log("swag shop API running on port 3002");
});

app.post('/product',function(req,res){
    var product = new Product();
    product.title = req.body.title;
    product.price = req.body.price;
    product.save(function(err, savedProduct){
        if (err){
            res.status(500).send({error:'could not save product'});
        }else{
            res.send(savedProduct);
        }
    });
    
});

app.get('/product',function(req,res){
    Product.find({},function(err,products){
        if(err){
            res.send({error:'could not fetch products'});
        }else{
            res.send(products);
        }
    });

});

app.post('/wishList',function(req,res){
    var wishList = new WishList();
    wishList.title = req.body.title;
    wishList.save(function(err,newWishlist){
        if(err){
            res.send({error:'could not fetch products'});
        }else{
            res.send(newWishlist);
        }
    })
});


app.get('/wishlist', function(req,res){
    WishList.find({}).populate({path: 'products',model:'Product'}).exec(function(err,wishLists)
    {
        if(err){
        res.status(500).send({error: 'could not fetch wishlists'});
        }else{
            res.send(wishLists);
        }
    })
});
//we are defining the path and model that has to be populated. Path comes from the wishlist.js file which contains 'products' while model is retrive from the product.js where the fields or data of the object are stored.Then we execute using the exec keyword and return the wishlists along with the data.


app.put('/wishlist/add',function(req,res){
    Product.findOne({_id: req.body.productId}, function(err, product){
        if(err){
            res.send({error:'could not add item to the wishlist'});
        }else{
            WishList.update({_id: req.body.wishListId}, {$addToSet: {products: product._id}})
//            ,function(err,wishList){
//               if(err){
//                   res.send({error:'wishlist could not be updated'});
//               }else{
//                   res.send("added to wishlist successfully");
//               }
            }//updating the user specified wishlistId with the found product
        })
    })