1. Updating in the same ISession
Transactional persistent instances (ie. objects loaded, saved, created or queried by the ISession) may be manipulated by the application and any changes to persistent state will be persisted when the ISession is flushed (discussed later in this chapter). So the most straightforward way to update the state of an object is to Load() it, and then manipulate it directly, while the ISession is open:
DomesticCat cat = (DomesticCat) sess.Load( typeof(Cat), 69L );
cat.Name = "PK";
sess.Flush(); // changes to cat are automatically detected and persisted
Sometimes this programming model is inefficient since it would require both an SQL SELECT (to load an object) and an SQL UPDATE (to persist its updated state) in the same session. Therefore NHibernate offers an alternate approach.
2. Updating detached objects
Many applications need to retrieve an object in one transaction, send it to the UI layer for manipulation, then save the changes in a new transaction. (Applications that use this kind of approach in a high-concurrency environment usually use versioned data to ensure transaction isolation.) This approach requires a slightly different programming model to the one described in the last section. NHibernate supports this model by providing the method Session.Update().
// in the first session
Cat cat = (Cat) firstSession.Load(typeof(Cat), catId);
Cat potentialMate = new Cat();
firstSession.Save(potentialMate);
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