+2  A: 

You don't need to load the references from the DB.

If you have the ID, session.Load<TheEntity>(theId) returns a proxy for the requested entity and Id without going to the DB.

Diego Mijelshon
Hi, that is not what i meant.
If a have an address, with cityID 5. I get<Address>(5), no problem. the city property is NOT loaded. Than i serialize it to the client (n-tier). Client changes some properties, but not the city. When i receive the object back, city has a vlue o NULL offcource, bacause it was not loaded earlier.
dam. i was not finished. So on arrival from client, city property after serialization is null. When is save it in NH, it will remove my city reference in the database. So, as it seems, before every Update(entity), i have to load all references back.....