Can't delete many-to-one relationship in NHibernate. Constraint Error
I have the following mapping in Fluent NHibernate:

    public class SubEventMap : ClassMap<SubEvent>
    {
        public SubEventMap()
        {
            Id(x => x.ID).GeneratedBy.HiLo("1000");
            Map(x => x.Name);
            References(x => x.Project)
                .Not.Nullable()
                .Cascade.All();
            References(x => x.Place)
                .Not.Nullable()
                .Cascade.SaveUpdate();
            Map(x => x.BeginDate);
            Map(x => x.EndDate);
            Map(x => x.Description);
        }
    }
	
    public class ReservationMap : ClassMap<Reservation>
    {
        public ReservationMap()
        {
            Id(x => x.ID).GeneratedBy.HiLo("1000");
            References(x => x.Customer)
            References(x => x.SubEvent)
        }
    }
	
    public class EventMap : ClassMap<Event>
    {
        public EventMap()
        {
            Id(x => x.ID).GeneratedBy.HiLo("1000");
            Map(x => x.Name);
            Map(x => x.BeginDate);
            Map(x => x.EndDate);
            Map(x => x.Description);
            Map(x => x.ImageUrl);
            HasMany(x => x.SubEvents)
                .Cascade.All();
            References(x => x.Place)
                .Cascade.SaveUpdate();
        }
    }

My problem arises when I want to delete a SubEvent Entity. Then I get the following error:
The DELETE statement conflicted with the REFERENCE constraint "FKC6A3305D965F624D". The conflict occurred in database "EMS", table "dbo.Reservation", column 'SubEvent_id'.
The statement has been terminated.

How can I change my mapping to prevent this error on subevent deletion and cascade the deletion of reservations?
Can't delete many-to-one relationship in NHibernate. Constraint Error
===

I have the following mapping in Fluent NHibernate:

    public class SubEventMap : ClassMap<SubEvent>
    {
        public SubEventMap()
        {
            Id(x => x.ID).GeneratedBy.HiLo("1000");
            Map(x => x.Name);
            References(x => x.Project)
                .Not.Nullable()
                .Cascade.All();
            References(x => x.Place)
                .Not.Nullable()
                .Cascade.SaveUpdate();
            Map(x => x.BeginDate);
            Map(x => x.EndDate);
            Map(x => x.Description);
        }
    }
	
    public class ReservationMap : ClassMap<Reservation>
    {
        public ReservationMap()
        {
            Id(x => x.ID).GeneratedBy.HiLo("1000");
            References(x => x.Customer)
            References(x => x.SubEvent)
        }
    }
	
    public class EventMap : ClassMap<Event>
    {
        public EventMap()
        {
            Id(x => x.ID).GeneratedBy.HiLo("1000");
            Map(x => x.Name);
            Map(x => x.BeginDate);
            Map(x => x.EndDate);
            Map(x => x.Description);
            Map(x => x.ImageUrl);
            HasMany(x => x.SubEvents)
                .Cascade.All();
            References(x => x.Place)
                .Cascade.SaveUpdate();
        }
    }

My problem arises when I want to delete a SubEvent Entity. Then I get the following error:
The DELETE statement conflicted with the REFERENCE constraint "FKC6A3305D965F624D". The conflict occurred in database "EMS", table "dbo.Reservation", column 'SubEvent_id'.
The statement has been terminated.

How can I change my mapping to prevent this error on subevent deletion and cascade the deletion of reservations?