db={"orders":[{"_id":ObjectId("607fbeeb0a752a66a7af40eb"),"address":{"loc":[-1,3],"_id":"5d35d55d3d081f486d0d401c","apartment":"","description":"ACcdg dfef"},"approvedAt":ISODate("2021-04-21T11:28:05.295+05:30"),"assignedAt":null,"billingAddress":{"description":""},"createdAt":ISODate("2021-04-21T11:28:04.449+05:30"),"creditCard":"","deliveryDate":"04/21/21","deliveryDateObj":ISODate("2021-04-21T12:27:58.746+05:30"),"owner":"609bd5831b912947ea51a9ac","products":["5a070c079b"],"updatedAt":ISODate("2021-04-21T11:28:05.295+05:30")}],"users":[{"_id":ObjectId("609bd5831b912947ea51a9ac"),"updatedAt":ISODate("2021-05-12T18:47:55.291+05:30"),"createdAt":ISODate("2021-05-12T18:47:55.213+05:30"),"email":"1012@gmail.com","phone":"123","dob":"1996-04-10","password":"","stripeID":"","__t":"Customer","name":{"first":"A","last":"b"},"orderCount":1,"__v":0,"forgottenPassword":""}]}

db.users.aggregate([{"$lookup":{"from":"orders","let":{"id":{$toString:"$_id"}},"pipeline":[{"$match":{$expr:{$eq:["$owner","$$id"]}}},{$project:{_id:0,createdAt:1}}],"as":"orders"}},{$project:{email:1,name:1,orderCount:{$size:"$orders"},phone:1,lastOrder:{$max:"$orders.createdAt"}}}])