title: $lookup with nested array of objects
body: <p>My document  has array with multiple objects, And I need to find related values and push into same array. </p>
  
  <p><strong>CART</strong></p>
  
  <pre><code>{
      "_id" : ObjectId("5b2b72119fbb60750e0061b9"),
      "cartId" : "1529573905701",
      "supplierId" : ObjectId("5b221d1b63eda2902418434d"),
      "user_id" : "5b20c54651e68057b3cbe745",
      "createdAt" : ISODate("2018-06-21T09:38:25.680Z"),
      "services" : [ 
          {
              "date" : "21-06-2018",
              "timeSlot_id" : ObjectId("5b29e08cb116c31f5b1f56c6"),
              "time" : "03:30 PM - 04:30 PM",
              "serviceId" : ObjectId("5b24aff4abf2494701bc1c15"),
              "cost" : 250,
              "_id" : ObjectId("5b2b72119fbb60750e0061ba")
          }, 
          {
              "_id" : ObjectId("5b2b72329fbb60750e0061bb"),
              "cost" : 250,
              "serviceId" : ObjectId("5b24aff4abf2494701bc1c15"),
              "time" : "03:30 PM - 04:30 PM",
              "timeSlot_id" : ObjectId("5b29e08cb116c31f5b1f56c6"),
              "date" : "21-06-2018"
          }
      ],
      "__v" : 0
  } 
  </code></pre>
  
  <p><strong>SERVICES</strong></p>
  
  <pre><code>{
      "_id" : ObjectId("5b24aff4abf2494701bc1c15"),
      "isActivated" : true,
      "supplierServiceId" : 900146649,
      "serviceId" : 99473640,
      "serviceName" : "AC Reparing",
      "description" : "all type of AC, Split AC and Window AC",
      "cost" : 250,
      "serviceDuration" : "60",
      "startTime" : "07:00 AM",
      "endTime" : "08:30 PM",
      "supplierId" : "5b221d1b63eda2902418434d",
      "createdAt" : ISODate("2018-06-16T06:36:36.091Z"),
      "__v" : 0
  }
  </code></pre>
  
  <p><strong>TIMESLOTS</strong></p>
  
  <pre><code>{
      "_id" : ObjectId("5b29e08cb116c31f5b1f56c6"),
      "displayString" : "03:30 PM - 04:30 PM",
      "isActivated" : true,
      "startTime" : "15:30 PM",
      "endTime" : "16:30 PM",
      "duration" : "60",
      "createdAt" : ISODate("2018-06-20T05:05:16.405Z"),
      "__v" : 0
  }
  </code></pre>
  
  <p>Inside the services in <strong>CART</strong> there are two values <strong>serviceId</strong> and <strong>timeSlot_id</strong></p>
  
  <p>*I need data related to both from related collections. Within same object.</p>
  
  <p>Mongo version -v3.6.5</p>
  
  <p>Please Help to solve this. Thanks in advance.</p>