> use test
switched to db test
> db.main.find()
{"_id" : "b45c046c-c502-11dd-b0b6-001d7dc91168" , "_ref" : {"$ref" : "test" , "$id" : "b44ab2b6-c502-11dd-b0b6-001d7dc91168"}}
> db.test.find()

{"_id" : "b44ab2b6-c502-11dd-b0b6-001d7dc91168"}

> db.main.find(

{"_ref": DBRef('test', 'b44ab2b6-c502-11dd-b0b6-001d7dc91168')}

)
Wed Aug 19 10:01:05 JS Error: Error: 2nd arg to DBRef needs to be oid (shell):0