NHibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance before flushing: Com.WildTangent.ProductCatalog.Data.RuleGroupSlot at NHibernate.Impl.SessionImpl.ThrowTransientObjectException(Object obj) at NHibernate.Impl.SessionImpl.GetEntityIdentifierIfNotUnsaved(Object obj) at NHibernate.Type.EntityType.GetIdentifier(Object value, ISessionImplementor session) at NHibernate.Type.ManyToOneType.NullSafeSet(IDbCommand cmd, Object value, Int32 index, ISessionImplementor session) at NHibernate.Collection.AbstractCollectionPersister.WriteElement(IDbCommand st, Object elt, Boolean writeOrder, ISessionImplementor session) at NHibernate.Collection.Map.WriteTo(IDbCommand st, ICollectionPersister persister, Object entry, Int32 i, Boolean writeOrder) at NHibernate.Collection.AbstractCollectionPersister.Recreate(PersistentCollection collection, Object id, ISessionImplementor session) at NHibernate.Impl.ScheduledCollectionRecreate.Execute() at NHibernate.Impl.SessionImpl.Execute(IExecutable executable) at NHibernate.Impl.SessionImpl.ExecuteAll(IList list) at NHibernate.Impl.SessionImpl.Execute() at NHibernate.Impl.SessionImpl.Flush() at NHibernate.Transaction.AdoTransaction.Commit() at Com.WildTangent.NHibernateUtil.Persist.GenericNHibernateDAO`1.Persist(TemplateClass entity)

protected void SaveChanges(string catalogDescription)
{
   if (!StringUtil.IsBlank(catalogDescription)) {
      RuleGroupDAO ruleGroupDAO = new RuleGroupDAO();
      SlotDAO slotDAO = new SlotDAO();
      ProductDAO productDAO = new ProductDAO();

      RuleGroup ruleGroup = ruleGroupDAO.GetByDescription(catalogDescription);
      List<string> slotKeys = ProductSlotManagerMain.SlotKeys;

      // add / update all slots
      foreach (string slotKey in slotKeys) {
         Slot slot = slotDAO.GetByKey(slotKey);
         List<Product> productList = productDAO.GetProductsFromList(ProductSlotManagerMain.GetProductListBySlotKey(slotKey));
                        
         if (ruleGroup.RuleGroupSlots.Contains(slot)) {
            RuleGroupSlot ruleGroupSlot = (RuleGroupSlot)ruleGroup.RuleGroupSlots[slot];
            List<Product> existingProductList = ruleGroupSlot.GetOrderedProducts().Products;

            if (!CatalogUtil.ProductListsAreEqualByOrder(productList, existingProductList)) {
               ruleGroupSlot.OrderedProducts = productList;
               ruleGroup.RuleGroupSlots[slot] = ruleGroupSlot;
            }

         } else {
            if (productList.Count > 0) {
//********* fails when executing this code path
               RuleGroupSlot ruleGroupSlot = new RuleGroupSlot();
               ruleGroupSlot.OrderedProducts = productList;
               ruleGroupSlot.Slot = slot;
               ruleGroupSlot.RuleGroup = ruleGroup;
               ruleGroup.RuleGroupSlots.Add(slot, ruleGroupSlot);
            }
         }
      }

      ruleGroupDAO.Persist(ruleGroup);
//********* fails on persist (Save)
   }
}

<?xml version="1.0" encoding="utf-8" ?>

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0"
                   namespace="Com.WildTangent.ProductCatalog.Data"
                   assembly="ProductCatalog">
    <class name="RuleGroup" table="t_RuleGroup" lazy="true">
        <cache usage="read-write" />

        <id name="Id" column="RuleGroupId" type="int">
            <generator class="native" />
        </id>

      ... irrelevant stuff ...

        <map name="RuleGroupSlots" table="t_RuleGroupSlot" batch-size="50"  lazy="true" cascade="none">
            <key column="RuleGroupId" />
            <index-many-to-many class="Slot" column="SlotId" />
            <one-to-many class="RuleGroupSlot" />
        </map>

    </class>
</hibernate-mapping>

<?xml version="1.0" encoding="utf-8" ?>

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0"
                   namespace="Com.WildTangent.ProductCatalog.Data"
                   assembly="ProductCatalog">
    <class name="RuleGroupSlot" table="t_RuleGroupSlot" lazy="true">
        <cache usage="read-write" />

        <id name="Id" column="RuleGroupSlotId" type="int">
            <generator class="native" />
        </id>

        <list name="OrderedProducts" table="t_ProductSlotOrder">
            <key column="RuleGroupSlotId" />
         <index column="`Order`" />
            <many-to-many column="ProductId" class="Product" />
        </list>

    </class>
</hibernate-mapping>

public class RuleGroup
{
   public virtual int Id
   {
      get { return _id; }
      set { _id = value; }
   }

   public virtual IDictionary RuleGroupSlots
   {
      get { return _ruleGroupSlots; }
      set { _ruleGroupSlots = value; }
   }

   public virtual ICollection Slots
   {
      get
      {
         return _ruleGroupSlots.Keys;
      }
   }
   
   // omitted tons of stuff.. just included the relevant portion

   protected int _id;
   private IDictionary _ruleGroupSlots = new Dictionary<Slot, RuleGroupSlot>();
}

public class RuleGroupSlot
    {
        public virtual int Id
        {
            get { return _id; }
            set { _id = value; }
        }

        public virtual RuleGroup RuleGroup
        {
            get { return _ruleGroup; }
            set { _ruleGroup = value; }
        }

        public virtual Slot Slot
        {
            get { return _slot; }
            set { _slot = value; }
        }

        public IProductList GetOrderedProducts()
        {
            ProductList productList = new ProductList();
            productList.Products = CollectionsUtil.ToGenericList<Product>(OrderedProducts);
            return productList;
        }

        public virtual IList OrderedProducts
        {
            get { return _orderedProducts; }
            set
         {
            // remove null items which is caused when the product orders are not sequential
            for (int ii = value.Count - 1; ii >= 0; ii--) {
               if (value[ii] == null) {
                  value.RemoveAt(ii);
               }
            }

            _orderedProducts = value;
         }
        }

        public override bool Equals(object obj)
        {
            RuleGroupSlot other = obj as RuleGroupSlot;
            return other != null ? other.Slot == Slot && other.RuleGroup == RuleGroup : false;
        }

        public override int GetHashCode()
        {
            return typeof(RuleGroupSlot).GetHashCode() ^
                (Slot != null ? Slot.GetHashCode() : 0) ^
                (RuleGroup != null ? RuleGroup.GetHashCode() : 0);
        }

        private int _id;
        private IList _orderedProducts;
        private RuleGroup _ruleGroup;
        private Slot _slot;
    }