Using nHibernate and the repository pattern, need some direction

Question

Hi,

Ok so I 'm just getting into nhibernate (using fluent).

One thing that I love about it is that I can use the Repository pattern (read about it from the nhibernate rhino blog).

Basically using generics, I can create methods that will work accross ALL my database tables.

 public interface IRepository<T>
    {
        T GetById(int id);
        ICollection<T> FindAll();
        void Add(T entity);
        void Remove(T entity);
    }


 public class Repository<T> : IRepository<T>
    {

        public ISession Session
        {
            get 
            { 
                return SessionProvider.GetSession(); 
            }
        }


        public T GetById(int id)
        {
            return Session.Get<T>(id);
        }

        public ICollection<T> FindAll()
        {
            return Session.CreateCriteria(typeof(T)).List<T>();
        }

        public void Add(T t)
        {
            Session.Save(t);
        }

        public void Remove(T t)
        {
            Session.Delete(t);
        }    

    }

I then inherit the Repository class and I can then add methods that are specific to that entity.

When trying to add an Update method, someone mentioned that the Repository pattern is suppose to act on collections? Am I looking at things incorrectly here? Why can't I create an update method?

I tried adding a update method, but I'm confused as to how I will handle the session and update the database?

I want a single place for all my database access for each entity, so UserRepository will have all basic CRUD and then maybe some other methods like GetUserByEmail() etc.

Answer 1

Don't use the repository pattern - use the UnitOfWork pattern instead, and pass defined query ICriteria to the ISession. Essentially the Repo pattern is wrapping something that doesn't need to be wrapped with NH.

see http://ayende.com/Blog/archive/2009/04/17/repository-is-the-new-singleton.aspx for more info

Answer 2

Perhaps you misheard or someone mispoke - the Repository pattern is supposed to expose collection like behavior, not operate on collections. Just like you can add, remove and search for items in a collection, your repository offers save, delete and search operations that work against your database.

I suggest you download the code for S#arp Architecture. It includes a repository implementation that you can reuse quite easily. If you don't want to take the dependency, at the very least you can spend some time studying their implementation to give you a better idea of how to approach it yourself.