[{"clientNo":2,"activeSubNo":1,"upcomingSubNo":0,"subscriptions":[{"subNo":1,"Type":"FREE","startDate":ISODate("2021-09-02"),"endDate":ISODate("2021-11-02")},{"subNo":2,"Type":"PAID","startDate":ISODate("2021-12-02"),"endDate":ISODate("2022-02-04")},{"subNo":3,"Type":"PAID","startDate":ISODate("2022-02-05"),"endDate":ISODate("2022-05-04")}]},{"clientNo":5,"activeSubNo":2,"upcomingSubNo":0,"subscriptions":[{"subNo":1,"Type":"FREE","startDate":ISODate("2021-09-02"),"endDate":ISODate("2021-11-02")},{"subNo":2,"Type":"PAID","startDate":ISODate("2021-12-02"),"endDate":ISODate("2022-02-03")}]}]

db.collection.aggregate([{"$addFields":{"activeSubscription":{"$first":{"$filter":{"input":"$subscriptions","as":"s","cond":{$eq:["$$s.subNo","$activeSubNo"]}}}}}},])