Question

How should I have the NHibernate Session Factory and the sessions for a WinForms application?

Should the SessionFactory be a singleton? Or can I create it every time? What about sessions and transactions?

Any help would be appreciated. Thanks

Answer 1

The session factory should be a singleton since it is expensive to create. It is thread safe so there is no threading issue with using it.

I have used the session-per-conversation pattern in winforms applications, and have found it to work well. With this pattern you use the same session for a series of operations that belong together. As I see it, a conversation in a winforms app could, roughly, be mapped to a GUI operation in your application.

Using a new session for every GUI operation helps keep the session small enough to to avoid performance problems with to many entities in the first level cache, while at the same time avoiding using a separate session for every operation, which also can cause performance problems.

To implement this you then create a new session before handling the GUI command, and when the command has been handled you dispose the session. Below is an example of this, which uses a class (PersistenceContext) that creates a session when it is instantiated and disposes the session when it is disposed. This class can then create repositories that use the current session.

public void SomeGuiEvent(...)
{
    using (var context = new PersistenceContext())
    {
        ProcessStuff(context);
    }
}

There are ofcourse many other options of how to implement this, but however you choose to implement it, I can recommend the Session-per-conversation pattern when using NHibernate in a Winforms app.