NHibernate–Interceptor doesn’t work for inherited objects

I got some trouble with NHibernate. I created the following interceptor to update audit fields before saving changes to the database:

	public class NHibernateInterceptor : NHib.EmptyInterceptor
	{
	private readonly ILogger _logger;
	private readonly IUserFactory _userFactory;
	public NHibernateInterceptor(ILogger logger, IUserFactory userFactory)
	{
	_logger= logger;
	_userFactory = userFactory;
	}
	public override bool OnFlushDirty(object entity, object id, object[] currentState, object[] previousState, string[] propertyNames, global::NHibernate.Type.IType[] types)
	{
	if (entity is IAuditable auditable)
	{
	var updatedByIndex = Array.IndexOf(propertyNames, nameof(IAuditable.UpdatedBy));
	var updatedOnIndex = Array.IndexOf(propertyNames, nameof(IAuditable.UpdatedOn));
	currentState[updatedByIndex] = auditable.UpdatedBy = _userFactory.GetCurrentUser().Id;
	currentState[updatedOnIndex] = auditable.UpdatedOn = DateTime.Now;
	}
	return base.OnFlushDirty(entity, id, currentState, previousState, propertyNames, types);
	}
	public override bool OnSave(object entity, object id, object[] state, string[] propertyNames, global::NHibernate.Type.IType[] types)
	{
	if (entity is IAuditable auditable)
	{
	var createdByIndex = Array.IndexOf(propertyNames, nameof(IAuditable.CreatedBy));
	var createdOnIndex = Array.IndexOf(propertyNames, nameof(IAuditable.CreatedOn));
	var updatedByIndex = Array.IndexOf(propertyNames, nameof(IAuditable.UpdatedBy));
	var updatedOnIndex = Array.IndexOf(propertyNames, nameof(IAuditable.UpdatedOn));
	var now = DateTime.UtcNow;
	state[createdByIndex] = auditable.CreatedBy = _userFactory.GetCurrentUser().Id;
	state[createdOnIndex] = auditable.CreatedOn = now;
	state[updatedByIndex] = auditable.UpdatedBy = _userFactory.GetCurrentUser().Id;
	state[updatedOnIndex] = auditable.UpdatedOn = now;
	}
	return base.OnSave(entity, id, state, propertyNames, types);
	}
	}

view raw NHibernateInterceptor.cs hosted with ❤ by GitHub

This interceptor does it’s job for simple objects but seems not to work for inherited objects:

	public class CategoryMap : ClassMap<Category>
	{
	public CategoryMap()
	{
	Table("Categories");
	Id(p => p.Id, "CategoryID");
	Map(p => p.CategoryName).Not.Nullable();
	Map(p => p.Description);
	Map(p => p.Picture);
	Map(e => e.CreatedOn).Not.Nullable();
	Map(e => e.CreatedBy).Not.Nullable();
	Map(e => e.UpdatedOn).Not.Nullable();
	Map(e => e.UpdatedBy).Not.Nullable();
	}
	}

view raw CategoryMap.cs hosted with ❤ by GitHub

	public class PremiumCategoryMap: SubclassMap<PremiumCategory>
	{
	public PremiumCategoryMap()
	{
	Table("PremiumCategory");
	KeyColumn("Id");
	Map(c => c.PremiumLevel).Not.Nullable();
	}
	}

view raw PremiumCategoryMap.cs hosted with ❤ by GitHub

To get it working I had to change the interceptor to always return true in the OnSave and OnFlushDirty methods:

	public class NHibernateInterceptor : NHib.EmptyInterceptor
	{
	private readonly ILogger _logger;
	private readonly IUserFactory _userFactory;
	public NHibernateInterceptor(ILogger logger, IUserFactory userFactory)
	{
	_logger= logger;
	_userFactory = userFactory;
	}
	public override bool OnFlushDirty(object entity, object id, object[] currentState, object[] previousState, string[] propertyNames, global::NHibernate.Type.IType[] types)
	{
	if (entity is IAuditable auditable)
	{
	var updatedByIndex = Array.IndexOf(propertyNames, nameof(IAuditable.UpdatedBy));
	var updatedOnIndex = Array.IndexOf(propertyNames, nameof(IAuditable.UpdatedOn));
	currentState[updatedByIndex] = auditable.UpdatedBy = _userFactory.GetCurrentUser().Id;
	currentState[updatedOnIndex] = auditable.UpdatedOn = DateTime.Now;
	//Return true to always trigger update of the fields
	return true;
	}
	return base.OnFlushDirty(entity, id, currentState, previousState, propertyNames, types);
	}
	public override bool OnSave(object entity, object id, object[] state, string[] propertyNames, global::NHibernate.Type.IType[] types)
	{
	if (entity is IAuditable auditable)
	{
	var createdByIndex = Array.IndexOf(propertyNames, nameof(IAuditable.CreatedBy));
	var createdOnIndex = Array.IndexOf(propertyNames, nameof(IAuditable.CreatedOn));
	var updatedByIndex = Array.IndexOf(propertyNames, nameof(IAuditable.UpdatedBy));
	var updatedOnIndex = Array.IndexOf(propertyNames, nameof(IAuditable.UpdatedOn));
	var now = DateTime.UtcNow;
	state[createdByIndex] = auditable.CreatedBy = _userFactory.GetCurrentUser().Id;
	state[createdOnIndex] = auditable.CreatedOn = now;
	state[updatedByIndex] = auditable.UpdatedBy = _userFactory.GetCurrentUser().Id;
	state[updatedOnIndex] = auditable.UpdatedOn = now;
	//Return true to always trigger update of the fields
	return true;
	}
	return base.OnSave(entity, id, state, propertyNames, types);
	}
	}

view raw NHibernateInterceptorFixed.cs hosted with ❤ by GitHub