OO Databases that Pass by reference?

I have played with MongoDB a little and wondered is there every going to be, or can there even be a database which passes by reference or pointer.

E.g. I have a single user instance which can be put into multiple ot开发者_运维问答her arrays, if you change it once in one place it changes in all arrays.

I understand that in a database you don't want your data flung all over the disk but might we ever see one?

I would venture to guess you are accidentally creating multiple references when using MongoDB. There seems to be little value in creating a Graph for the database in which none of the nodes are shared.

I have used db4o and it will maintain a single instance of an object such that if you change it, then reference it from another Object the change will be "reflected." I put that in quotes because they should be the same object due to the way graphs work.