title: how to get only subdocument from document query in mongoose
body: <p>I am trying to get only subdocument out of whole document via mongoose in node.js.
  My database schema is as follows:</p>
  
  <pre><code>var mongoose = require('mongoose');
  var Schema = mongoose.Schema;
  // var Items = require('./items.js');
  
  var Items = new Schema({
      no_of_times_ordered:Number,
      item_name:String,
      item_tag:String,
      item_category:String,
      item_stock:Number,
      item_price:Number,
      item_img:String,
      item_illustrations:[String],
      item_liked:Boolean,
      no_of_likes:Number
  },{ versionKey: false });
  
  
  var FoodTruckSchema = new Schema({
      foodtruck_name:String,
      foodtruck_location:String,
      foodtruck_rating:Number,
      foodtruck_tag:String,
      foodtruck_timing:String,
      foodtruck_cusine:String,
      foodtruck_img:String,
      foodtruck_logo:String,
      item_list: [Items]
  },{ versionKey: false });
  
  
  
  module.exports = mongoose.model('foodtruck',FoodTruckSchema);
  </code></pre>
  
  <p>The query is as given below:</p>
  
  <pre><code>var popularitems = function(req,res) {
      foodtr.find(function(err,items){
          if (err) res.send(err);
          res.json({
              status : '200',
              message:'popular items list',
              data: items
          });
      });
  </code></pre>
  
  <p>So I have already put query where items with foodtrucks are retrieved, but how can I only have items in response? </p>