[{"_id":"5b527a2bfadb811c4869e802","tasks":[{"done":false,"_id":"5b53494987eea4171d199dd3"},{"done":false,"_id":"5b53495087eea4171d199dd4"},{"done":false,"_id":"5b53495987eea4171d199dd5"}],"doneTasks_ids":["5b53494987eea4171d199dd3","5b53495087eea4171d199dd4"]},{"_id":"5b527a2ffadb811c4869e803","tasks":[{"done":false,"_id":"5b53496b87eea4171d199dd6"},{"done":false,"_id":"5b53497287eea4171d199dd7"}],"doneTasks_ids":["5b53497287eea4171d199dd7"]}]

db.collection.aggregate({"$addFields":{"tasks":{"$map":{"input":"$tasks","as":"task","in":{"_id":"$$task._id","done":{"$in":["$$task._id","$doneTasks_ids"]}}}}}})