> db.users.find()
{ "_id" : ObjectId("4fed6cfa70d4386442b9bb5a"), "name" : "Hett" }
{ "_id" : ObjectId("4fed6eb4886e91be45b14105"), "name" : "xxx", "manager" : { "$ref" : "users", "$id" : ObjectId("4fed6cfa70d4386442b9bb5a") } }
> db.users.find({'manager.name': 'Hett'})
>