NHibernate Best Practices with ASP.NET, 1.2nd Ed.

using System;
using System.Collections.Generic;
using NHibernate;
using NHibernate.Expression;
using ProjectBase.Utils;

namespace ProjectBase.Data
{
    public abstract class AbstractNHibernateDao<T, IdT> : IDao<T, IdT>
    {
        /// <param name="sessionFactoryConfigPath">Fully qualified path of the session factory's config file</param>
        public AbstractNHibernateDao(string sessionFactoryConfigPath) {
            Check.Require(! string.IsNullOrEmpty(sessionFactoryConfigPath),
                "sessionFactoryConfigPath may not be null nor empty");

            SessionFactoryConfigPath = sessionFactoryConfigPath;
        }

        /// <summary>
        /// Loads an instance of type T from the DB based on its ID.
        /// </summary>
        public T GetById(IdT id, bool shouldLock) {
            T entity;

            if (shouldLock) {
                entity = (T)NHibernateSession.Load(persitentType, id, LockMode.Upgrade);
            }
            else {
                entity = (T)NHibernateSession.Load(persitentType, id);
            }

            return entity;
        }

        /// <summary>
        /// Loads every instance of the requested type with no filtering.
        /// </summary>
        public List<T> GetAll() {
            return GetByCriteria();
        }

        /// <summary>
        /// Loads every instance of the requested type using the supplied <see cref="ICriterion" />.
        /// If no <see cref="ICriterion" /> is supplied, this behaves like <see cref="GetAll" />.
        /// </summary>
        public List<T> GetByCriteria(params ICriterion[] criterion) {
            ICriteria criteria = NHibernateSession.CreateCriteria(persitentType);

            foreach (ICriterion criterium in criterion) {
                criteria.Add(criterium);
            }

            return criteria.List<T>() as List<T>;
        }

        public List<T> GetByExample(T exampleInstance, params string[] propertiesToExclude) {
            ICriteria criteria = NHibernateSession.CreateCriteria(persitentType);
            Example example = Example.Create(exampleInstance);

            foreach (string propertyToExclude in propertiesToExclude) {
                example.ExcludeProperty(propertyToExclude);
            }

            criteria.Add(example);

            return criteria.List<T>() as List<T>;
        }

        /// <summary>
        /// Looks for a single instance using the example provided.
        /// </summary>
        /// <exception cref="NonUniqueResultException" />
        public T GetUniqueByExample(T exampleInstance, params string[] propertiesToExclude) {
            List<T> foundList = GetByExample(exampleInstance, propertiesToExclude);

            if (foundList.Count > 1) {
                throw new NonUniqueResultException(foundList.Count);
            }

            if (foundList.Count > 0) {
                return foundList[0];
            }
            else {
                return default(T);
            }
        }

        /// <summary>
        /// For entities that have assigned ID's, you must explicitly call Save to add a new one.
        /// See http://www.hibernate.org/hib_docs/reference/en/html/mapping.html#mapping-declaration-id-assigned.
        /// </summary>
        public T Save(T entity) {
            NHibernateSession.Save(entity);
            return entity;
        }

        /// <summary>
        /// For entities with automatatically generated IDs, such as identity, SaveOrUpdate may 
        /// be called when saving a new entity.  SaveOrUpdate can also be called to _update_ any 
        /// entity, even if its ID is assigned.
        /// </summary>
        public T SaveOrUpdate(T entity) {
            NHibernateSession.SaveOrUpdate(entity);
            return entity;
        }

        public void Delete(T entity) {
            NHibernateSession.Delete(entity);
        }

        /// <summary>
        /// Commits changes regardless of whether there's an open transaction or not
        /// </summary>
        public void CommitChanges() {
            if (NHibernateSessionManager.Instance.HasOpenTransactionOn(SessionFactoryConfigPath)) {
                NHibernateSessionManager.Instance.CommitTransactionOn(SessionFactoryConfigPath);
            }
            else {
                // If there's no transaction, just flush the changes
                NHibernateSessionManager.Instance.GetSessionFrom(SessionFactoryConfigPath).Flush();
            }
        }

        /// <summary>
        /// Exposes the ISession used within the DAO.
        /// </summary>
        private ISession NHibernateSession {
            get {
                return NHibernateSessionManager.Instance.GetSessionFrom(SessionFactoryConfigPath);
            }
        }

        private Type persitentType = typeof(T);
        protected readonly string SessionFactoryConfigPath;
    }
}