Finding Dirty Properties in NHibernate

Sometimes there may be a need for finding out if a specific entity, or a property of that entity, was changed, or, better yet, the original value for that property.

Below is a set of extensions for ISession that give you just that.

public static class SessionExtensions
	{
		public static Boolean IsDirtyEntity(this ISession session, Object entity)
		{
			String className = NHibernateProxyHelper.GuessClass(entity).FullName;
			ISessionImplementor sessionImpl = session.GetSessionImplementation();
			IPersistenceContext persistenceContext = sessionImpl.PersistenceContext;
			IEntityPersister persister = sessionImpl.Factory.GetEntityPersister(className);
			EntityEntry oldEntry = sessionImpl.PersistenceContext.GetEntry(entity);

			if ((oldEntry == null) && (entity is INHibernateProxy))
			{
				INHibernateProxy proxy = entity as INHibernateProxy;
				Object obj = sessionImpl.PersistenceContext.Unproxy(proxy);
				oldEntry = sessionImpl.PersistenceContext.GetEntry(obj);
			}

			Object [] oldState = oldEntry.LoadedState;
			Object [] currentState = persister.GetPropertyValues(entity, sessionImpl.EntityMode);
			Int32 [] dirtyProps = persister.FindDirty(currentState, oldState, entity, sessionImpl);
			
			return (dirtyProps != null);
		}

		public static Boolean IsDirtyProperty(this ISession session, Object entity, String propertyName)
		{
			String className = NHibernateProxyHelper.GuessClass(entity).FullName;
			ISessionImplementor sessionImpl = session.GetSessionImplementation();
			IPersistenceContext persistenceContext = sessionImpl.PersistenceContext;
			IEntityPersister persister = sessionImpl.Factory.GetEntityPersister(className);
			EntityEntry oldEntry = sessionImpl.PersistenceContext.GetEntry(entity);

			if ((oldEntry == null) && (entity is INHibernateProxy))
			{
				INHibernateProxy proxy = entity as INHibernateProxy;
				Object obj = sessionImpl.PersistenceContext.Unproxy(proxy);
				oldEntry = sessionImpl.PersistenceContext.GetEntry(obj);
			}

			Object [] oldState = oldEntry.LoadedState;
			Object [] currentState = persister.GetPropertyValues(entity, sessionImpl.EntityMode);
			Int32 [] dirtyProps = persister.FindDirty(currentState, oldState, entity, sessionImpl);
			Int32 index = Array.IndexOf(persister.PropertyNames, propertyName);

			Boolean isDirty = (dirtyProps != null) ? (Array.IndexOf(dirtyProps, index) != -1) : false;

			return (isDirty);
		}

		public static Object GetOriginalEntityProperty(this ISession session, Object entity, String propertyName)
		{
			String className = NHibernateProxyHelper.GuessClass(entity).FullName;
			ISessionImplementor sessionImpl = session.GetSessionImplementation();
			IPersistenceContext persistenceContext = sessionImpl.PersistenceContext;
			IEntityPersister persister = sessionImpl.Factory.GetEntityPersister(className);
			EntityEntry oldEntry = sessionImpl.PersistenceContext.GetEntry(entity);

			if ((oldEntry == null) && (entity is INHibernateProxy))
			{
				INHibernateProxy proxy = entity as INHibernateProxy;
				Object obj = sessionImpl.PersistenceContext.Unproxy(proxy);
				oldEntry = sessionImpl.PersistenceContext.GetEntry(obj);
			}

			Object [] oldState = oldEntry.LoadedState;
			Object [] currentState = persister.GetPropertyValues(entity, sessionImpl.EntityMode);
			Int32 [] dirtyProps = persister.FindDirty(currentState, oldState, entity, sessionImpl);
			Int32 index = Array.IndexOf(persister.PropertyNames, propertyName);

			Boolean isDirty = (dirtyProps != null) ? (Array.IndexOf(dirtyProps, index) != -1) : false;

			return ((isDirty == true) ? oldState [ index ] : currentState [ index ]);
		}
	}