[{_id:ObjectId("643f8a6773a92fb1552e4c89"),studentName:"Peter Jackson",studentId:"SID1001",grade:2,gender:"Male",parentDetails:[{_id:ObjectId("63fee5a42f60946679146768"),name:"Jackson Steve",email:"jack.steve@gmail.com",mobile:"xxxxxxxxxx",relation:"Father"},{_id:ObjectId("6447c1ba22670472ed4b29cc"),name:"Amenda Jackson",email:"amenda.jack@gmail.com",mobile:"xxxxxxxxxx",relation:"Mother"}]}]

db.collection.aggregate([{$unwind:"$parentDetails"},{$project:{studentName:1,studentId:1,grade:1,parentName:"$parentDetails.name",parentEmail:"$parentDetails.email",relation:"$parentDetails.relation"}}])