Question

I’m using NHibernate to do database access in my application. My ISessions have no persistance, and I’m happy with this as it makes it easier for me to separate my application into different layers. The only difficulty is dealing with lazy loading in a nice way.

I have a model class that looks like this:

public class User {
    public virtual int Id { get; set; }
    public virtual string Name { get; set; }
    public virtual Country CountryOfBirth { get; set }
    public virtual Country CountryOfResidence {get; set; }
}

At the moment, I have CountryOfBirth and CountryOfResidence set to fetch="join". However, as the list of countries in my database is mostly static, I want to cache these values. I changed the CountryOfBirth property to look like this:

    Country countryOfBirth;
    public virtual Country CountryOfBirth{
        get
        {
            if (country is INHibernateProxy)
                countryOfBirth = CountryRepository.GetById(countryOfBirth.Id);
            return countryOfBirth;
        }
        set { countryOfBirth = value; }
    }

However, it requires my Model class to know that it is being used by NHibernate, which breaks encapsulation.

Is there a better way to achieve this? For instance, is there a way to get NHibernate to automatically go through my Repository classes if it tries to load a proxy and the session has expired?

Or should I use a different method?

Answer 1

If you want to add cache capabilities then look at NHibernate L2 Cache. Check this tutorial http://nhforge.org/blogs/nhibernate/archive/2009/02/09/quickly-setting-up-and-using-nhibernate-s-second-level-cache.aspx and search for this topic. By using cache you don’t polute your model with any NH proxies, repositories, etc.