Database
db={"carDatas":[{carData:[{vin:123456789,make:"Dodge"},{vin:987654321,make:"Honda"}]}],"Vins":[{_id:ObjectId("123456123456123456123456"),Vin:123456789},{_id:ObjectId("123456123456123456123457"),Vin:987654321}]}
Query
db.carDatas.aggregate([{$unwind:"$carData"},{$lookup:{from:"Vins",localField:"carData.vin",foreignField:"Vin",as:"docs"}},{$project:{make:"$carData.make",vin:{$first:"$docs._id"},_id:0}},{$group:{_id:null,carData:{$push:"$$ROOT"}}},{$unset:"_id"}])