lookup in mongodb array

1> db.demo396.aggregate([
2...    { "$lookup": {
3...       "from": "demo395",
4...       "let": { "details": "$details" },
5...       "pipeline": [
6...          { "$match": { "$expr": { "$in": [ "$_id", "$$details" ] } } }
7...       ],
8...       "as": "output"
9...    }}
10... ])

1{ "_id" : ObjectId("5e5e787817aa3ef9ab8ab209"), "details" : [ ObjectId("5e5e782317aa3ef9ab8ab207"), ObjectId("5e5e782317aa3ef9ab8ab208") ], "output" : [ { "_id" : ObjectId("5e5e782317aa3ef9ab8ab207"), "Name" : "Chris" }, { "_id" : ObjectId("5e5e782317aa3ef9ab8ab208"), "Name" : "David" } ] }