title: lookup mongodb not working as e
body: <p>Order and riders this collections I have created with data
  riders</p>
  
  <pre><code>[
    {
      "_id": "5a55b5fb99391a1694fa4541",
      "name": "rider4",
      "email": "rider4@gmail.com",
      "mob": "3d4",
      "city": "Sotland",
      "address": "UK",
      "postcode": "411041",
      "password": "123456",
      "__v": 0,
      "device_token": "d12223",
      "status": false
    },
    {
      "_id": "5a55b5e399391a1694fa453f",
      "name": "rider2",
      "email": "rider2@gmail.com",
      "mob": "34",
      "city": "Sotland",
      "address": "UK",
      "postcode": "411041",
      "password": "123456",
      "__v": 0,
      "device_token": "12223",
      "status": false
    },
    {
      "_id": "5a55b5a299391a1694fa453a",
      "name": "rider3",
      "email": "rider3@gmail.com",
      "mob": "2",
      "city": "Sotland",
      "address": "UK",
      "postcode": "411041",
      "password": "123456",
      "__v": 0,
      "device_token": "123",
      "status": false
    },
    {
      "_id": "5a5453a76b7be60004bc8e67",
      "name": "rider1",
      "email": "rider1@gmail.com",
      "mob": "62345674d890",
      "city": "Sotland",
      "address": "UK",
      "postcode": "411041",
      "password": "123456",
      "__v": 0,
      "device_token": "123",
      "status": false
    }
  ]
  </code></pre>
  
  <p>Order collections has:</p>
  
  <pre><code>    {
          "_id": "5a599b750cdf310004334087",
          "orderNumber": "1",
          "riderId": "5a55b5e399391a1694fa453f"
      },
      {
          "_id": "5a599b600cdf310004334086",
          "orderNumber": "1",
          "riderId": "5a55b5a299391a1694fa453a"
      },
      {
          "_id": "5a599b380cdf310004334085",
          "orderNumber": "1",
          "riderId": "5a5453a76b7be60004bc8e67"
      },
      {
          "_id": "5a599b0c0cdf310004334084",
          "orderNumber": "1",
          "riderId": "5a55b5fb99391a1694fa4541"
      },
      {
          "_id": "5a599af30cdf310004334083",
          "orderNumber": "1",
          "riderId": "5a55b5fb99391a1694fa4541"
      },
      {
          "_id": "5a599ad90cdf310004334082",
          "orderNumber": "1",
          "riderId": "5a55b5e399391a1694fa453f"
      },
      {
          "_id": "5a599ac00cdf310004334081",
          "orderNumber": "1",
          "riderId": "5a55b5a299391a1694fa453a"
      },
  </code></pre>
  
  <p>I am running these queries:</p>
  
  <pre><code>db.getCollection('orders').aggregate([
                {$match:{'order_created':"1/13/18" }},
                 {$lookup:{"from":"rider","localField":"riderId", 
  "foreignField":"RID","as":"rider"}}])
  </code></pre>
  
  <p>It shows output </p>
  
  <pre><code>rider : 0
  </code></pre>