Database
db={category:[{"image":"http://res.cloudinary.com/wisecart/image/upload/v1616718691/kuy26lytx5k0lkvfkgrt.svg","_id":"606605934b213d2887e3a840","name":"Samsung","description":"sama","id":"asa","created":"2021-04-01T17:40:35.505Z","__v":0}],subCategory:[{name:"a1",category:"606605934b213d2887e3a840"},{name:"a2",category:"606605934b213d2887e3a840"}]}
Query
db.category.aggregate([{"$lookup":{"from":"subCategory","localField":"_id","foreignField":"category","as":"subCategory"}}])