Fluent NHibernate ISessionManager or equivilent

Question

I am quite new to the FNH and NH world, so be gentle :P

I have created an application using FNH for data access which works good while not using lazy-loading, however once I enable lazy-loading everything goes pear shaped (as in, no sessions are open when I attempt to access the lazy-loaded properties etc).

The application layout I have created thus-far has a "Database" singleton which has various methods such as Save(), Refer() and List().
When calling Refer() a session is opened, the data is retrieved and the session is disposed; meaning there is no session available when attempting to access a lazy-loaded property from the returned object. Example: Database.Refer("username").Person since Person is lazy-loaded and the session has already closed.

I have read that Castle has a SessionManager that could be used for this very scenario but, either it's the late nights or lack of coffee, I can't seem to work out how to hook up FNH to use this manager as, in the spirit of castle, everything is defined in config files.

Am I missing something, or can this not be done? Are there any other session managers (or even more appropriate conventions) that I should look at?

Thanks for any help on this matter.

Answer 1

I don't think that your particular problem is connected with the SessionManager as you've already mentioned that you are capable of starting a new session and disposing it whenever needed.

From what I can understand of your post is that you are trying to expose an entity to your view (with some lazy-loaded properties) - which is already a bad idea because it leads to nasty LazyInitializationException(s).

You should consider making a distinguishion between your data-model and your domain model. The key concept has been described on this blog:

Ayende @ Rahien http://ayende.com/blog/4054/nhibernate-query-only-properties

If you say that you are writing a very simple 2-tier application then it probably will not harm if you will micro-manage your session in the data-layer (but keep in mind that this is not the best solution).

I would also look into the query that fetches your entity, as it seems to me that your are trying to obtain data that is just a part of your model - in this case Person. This can lead into serious problems like n+1 selects:

What is SELECT N+1?

So in general I think you should focus more on how things are structured in your application instead of searching for a SessionManager as it will not resolve all of your problems.

Answer 2

For any of you who are still looking for answers on this, I will share with you what I have so far.

This is only a very simple overview of the framework that I have decided to use, and is by far not the only solution for this problem.

The basic layout of my code is as follows:

• NHibernate Repository (references my model assembly and the UoW assembly)
  • Based on the HibernatingRhino's Repository implementation modified to suit my needs. Found here: http://ayende.com/Wiki/Rhino+Commons.ashx

    public T Get(Guid Id)
    {
        return WrapUOW(() =>
        {
            using (Audit.LockAudit())
                return (T)Session.Get(typeof(T), Id);
        });
    }
    public void LoadFullObject(T partial)
    {
        if (partial == null)
            throw new ArgumentNullException("partial");
    
        if (partial.Id == Guid.Empty)
            return;
    
        WrapUOW(() =>
        {
            using (Audit.LockAudit())
            {
                LazyInitialiser.InitialiseCompletely(partial, Session);
            }
        });
    }
    public T SaveOrUpdate(T entity)
    {
        using (Audit.LockAudit())
        {
            With.Transaction(() =>
            {
                Enlist(entity);
    
                Session.SaveOrUpdate(entity);
    
                entity.HasChanged = false;
            });
        }
    
        return entity;
    }
    protected void Enlist(T instance)
    {
        if (instance != null && instance.Id != Guid.Empty && !Session.Contains(instance))
            using (Audit.LockAudit())
            {
                Session.Update(instance);
            }
    }
    
    

  • References a neat little helper class called 'Lazy Initializer for NHibernate' found here: http://www.codeproject.com/KB/cs/NHibernateLazyInitializer.aspx
  • This also contains Extension methods for Save, Delete and LoadFullObject
  • Have broken standards a little in this assembly by also creating a WrapUOW method to help simplify some of my code

    protected static T WrapUOW(Func action)
    {
        IUnitOfWork uow = null;
    
        if (!UnitOfWork.IsStarted)
            uow = UnitOfWork.Start();
    
        T result = action();
    
        if (uow != null)
            uow.Dispose();
    
        return result;
    }

• NHibernate Unit of work (references my model assembly)
  • Also based on the HibernatingRhino's UoW implementation and modified to suit
• View - not important, just requried for MVVM implementation
  • Binds the values from the ViewModel
• Model
  • Contains my entity classes and hibernate mapping files
• ViewModel
  • Contains two main view base classes, ListPage and MaintenancePage
  • The ListPage base class just calls the Repository List method based on the object type we are listing. This loads a dehydrated list of entities.
  • The MaintenancePage takes an entity instance from the ListPage and calls the Repository.LoadFullObject method to rehydrate the entity for use on the screen.
    • This allows for the use of binding on the screen.
    • We can also safely call the Repository.SaveOrUpdate method from this page