Question

I have two entities:

    public class Group
    {
        public virtual int Id { get; set; }
        public virtual string Name { get; set; }

        private ICollection<Item> _items = new HashSet<Item>();
        public virtual ICollection<Item> Items
        {
            get { return _items; }
            set { _items = value; }
        }
    }

    public class Item
    {
        public virtual int Id { get; set; }
        public virtual string Name { get; set; }
    }

I use automapping with the following override:

automapping.Override<Group>(m => m.HasManyToMany(_ => _.Items).AsSet());

I construct a group object and few items adding them to the group object. When I save the group object using session.Save(group) the exception occurs:

NHibernate.TransientObjectException: object references an unsaved transient instance – save the transient instance before flushing. Type: NhResearch.ManyToManyTests+Item, Entity: 0 item1
at NHibernate.Engine.ForeignKeys.GetEntityIdentifierIfNotUnsaved(String entityName, Object entity, ISessionImplementor session)

What am I missing here?

Answer 1

You’re missing a cascade setting.

m => m.HasManyToMany(_ => _.Items).AsSet().Cascade.AllDeleteOrphan()

All – if you want to save update and delete items

AllDeleteOrphan – same as all, but also deletes orphaned items

SaveUpdate – cascade on save or update

Delete – cascade only deleted items

FYI, you’re also likely missing the Table specification and the parent and child key columns.