[{"id":1,"name":"N1","tasks":{"project1":{"task7":{"count":10,"time":1.2},"task3":{"count":56,"time":1050}},"project25":{"task7":{"count":25,"time":10}}}},{"id":2,"name":"N1","tasks":{"project1":{"task70":{"count":10,"time":1.2},"task3":{"count":56,"time":1050}},"project25":{"task70":{"count":25,"time":10}}}},{"id":3,"name":"N1","tasks":{"project1":{"task70":{"count":10,"time":1.2},"task3":{"count":56,"time":1050}},"project25":{"task7":{"count":25,"time":10}}}}]

db.collection.aggregate([{$project:{_id:0,"id":1,"name":1,tasks:{$objectToArray:"$tasks"}}},{"$unwind":"$tasks"},{$project:{_id:0,"id":1,"name":1,"tasks.k":1,"tasks.v":{$objectToArray:"$tasks.v"}}},{"$unwind":"$tasks.v"},{"$match":{"tasks.v.k":"task7"}}])