问使用NHibernate实现复合键/Id映射

EN

Announcements:
- AnnouncementID (PK)
- Title

AnouncementsRead (composite PK on AnnouncementID and UserID):
- AnnouncementID (PK)
- UserID (PK)
- DateRead

Users:
- UserID (PK)
- UserName

    public class Announcement
    {
        public virtual int AnnouncementID { get; set; }
        public virtual string Title { get; set; }
        public virtual IList<AnnouncementRead> AnnouncementsRead { get; private set; }

        public Announcement()
        {
            AnnouncementsRead = new List<AnnouncementRead>();
        }
    }

    public class AnnouncementRead
    {
        public virtual Announcement Announcement { get; set; }
        public virtual User User { get; set; }
        public virtual DateTime DateRead { get; set; }
    }

    public class User
    {
        public virtual int UserID { get; set; }
        public virtual string UserName { get; set; }
        public virtual IList<AnnouncementRead> AnnouncementsRead { get; private set; }

        public User()
        {
            AnnouncementsRead = new List<AnnouncementRead>();
        }
 }

public class AnnouncementMap : ClassMap<Announcement>
{
    public AnnouncementMap()
    {
        Table("Announcements");
        Id(x => x.AnnouncementID);
        Map(x => x.Title);
        HasMany(x => x.AnnouncementsRead)
            .Cascade.All();
    }
}

public class AnnouncementReadMap : ClassMap<AnnouncementRead>
{
    public AnnouncementReadMap()
    {
        Table("AnnouncementsRead");
        CompositeId()
            .KeyReference(x => x.Announcement, "AnnouncementID")
            .KeyReference(x => x.User, "UserID");
        Map(x => x.DateRead);
    }
}

public class UserMap : ClassMap<User>
{
    public UserMap()
    {
        Table("Users");
        Id(x => x.UserID);
        Map(x => x.UserName);
        HasMany(x => x.AnnouncementsRead)
            .Cascade.All();
    }
}

"composite-id class must override Equals(): Entities.AnnouncementRead"