Mongo lookup to join a child/sub object?

Question

I am joining booking and customers collections. My bookings object looks like this:

   {
      "bookingID": 1,
      "customerID": "adam.apple@email.com",
      "room": [
         {
            "roomID": "JDS",
            "numRooms": 1
         }
      ]
   }

and customer object like this:

  {
     "customer": {
        "firstname": "Adam",
        "surname": "Apple",
        "title": "Nr.",
        "emailAddress": "adam.apple@email.com"
     },
     "address": {
        "street": "221B Baker St",
        "city": "London",
        "state": null,
        "zipcode": "NW1 6XE",
        "country": "UK"
     }
  }

I am using this code:

      { $lookup: {from: 'customers', localField: 'customerID', foreignField: 'customer.emailAddress', as: 'traveller'} },
      { $unwind: '$traveller' },
      { $project: {'traveller': {_id: 0, 'address': 0}} }

to combine the output. I'd like to get:

            "traveller": {
                "firstname": "Adam",
                "surname": "Apple",
                "title": "Nr.",
                "emailAddress": "adam.apple@email.com"
            }

and I get:

        "traveller": {
            "customer": {
                "firstname": "Adam",
                "surname": "Apple",
                "title": "Nr.",
                "emailAddress": "adam.apple@email.com"
            }
        }

How do I do this?

You can check it here: https://mongoplayground.net/p/ik2UtP4-EHa

Answer 1

Try this one its not break your other pipelines

aggregate([{
          $lookup: {
            from: 'customers', 
            localField: 'customerID', 
            foreignField: 'customer.emailAddress',
            as: 'traveller'
          } },
      { $unwind: '$traveller' },
      { $project: {
           'traveller':"$traveller.customer",
            bookingID:1,
            cruise:1,
          customerID:1,
          room:1,
          
          } }])

Answer 2

Here you go :-

Just change the project stage as below -

  {
    $project: {
      "traveller": "$traveller.customer",
      "bookingID": 1,
      "cruise": 1,
      "customerID": 1,
      "room": 1
    }
  }

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