Database
[{"id":1,"name":"sunil","Cars":[{"CarName":"skoda","type":"Petrol",}]},{"id":2,"name":"Kumar","Cars":[{"CarName":"skoda","type":"Petrol",},{"CarName":"benz","type":"Petrol",}]}]
Query
db.collection.aggregate([{"$match":{"id":2,"name":"Kumar"}},{"$project":{"_id":0,"size":{"$size":"$Cars"}}}])