Why do the MongoDB docs recommend not using DBREFs?
Here a conclusion of all I viewed.
Using DBRef is not a join operation, it will automatically query the second or more times, depends on how much DBRef you have got in this collection fields.
Assuming you have a collection that its model has 10 DBRef, you make query for 10 elements' list of it and one of these DBRef is really needed. Once you query, Mongodb will runs 101(1 + 10*10) queries, automatically, no matter you need these DBRef or not. If you query these field manually, just a few coding and only 11(1 + 1*10) queries are needed.
So, what do you say?