db={"person":[{name:"tom",favoriteFoods:[1,3]},],"foods":[{"_id":1,name:"banana"},{"_id":2,name:"apple"},{"_id":3,name:"pie"},]}

db.person.aggregate([{$match:{name:"tom"}},{"$lookup":{"from":"foods","localField":"favoriteFoods","foreignField":"_id","as":"favoriteFoods"}}])