Database
db={"movies":[{_id:"5d872b7f927f2538e4eefbf5",mvNumb:"1",Director:"5d8abd243372eb2850ad71e7"},{_id:"1r872b7f927f2538e4eef613",mvNumb:"2",Director:"721yabd243372eb2850ad7251"}],"directors":[{_id:"5d8abd243372eb2850ad71e7",Name:"Sam"}]}
Query
db.directors.aggregate([{$match:{Name:"Sam"}},{$lookup:{from:"movies",localField:"_id",foreignField:"Director",as:"movies"}},{$project:{_id:0,movies:1}}])