NHibernate: Querying on collection of strings (collection was not an association)

Question

Hello all.

I have this class that I want to persist with NHibernate. It has one collection, an IList, aggregating strings, rather than class instances, called DestinationCountryCodes.

  public class RoutingRule
  {
      public virtual long Id { get; set; }

      public virtual MessageType MessageType { get; set; }

      public virtual TransportMethod TransportMethod { get; set; }

      public virtual String Sender { get; set; }

      public virtual String Recipient { get; set; }

      public virtual IList<Party> Parties { get; set; }

      public virtual IList<String> DestinationCountryCodes { get; set; }

      public virtual string PickupCountryCode { get; set; }

      public virtual int PostalCodeLowerLimit { get; set; }

      public virtual int PostalCodeUpperLimit { get; set; }

      public virtual IList<DbConnectionEntry> DbConnectionEntries { get; set; }

      public virtual Boolean Ignore { get; set; }

etcetera....

This is how the mapping looks like:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" default-lazy="false">
  <class name="FargoGateLib.RoutingRule, FargoGateLib" 
         table="RoutingRules">
    <id name="Id" column="Id">
      <generator class="native" />
    </id>           
    <property name="MessageType" column="MessageType"/>
    <property name="TransportMethod" column="TransportMethod"/>
    <property name="Sender" column="Sender"/>
    <property name="Recipient" column="Recipient"/>
    <!--<property name="DestinationCountryCode" column="DestinationCountryCode"/>-->
    <bag name="DestinationCountryCodes" table="RoutingRuleCountryCodes" lazy="false" cascade="all">
      <key column="RoutingRuleID"/>
      <element column="CountryCode" type="System.String" />
    </bag>          
    <property name="PickupCountryCode" column="PickupCountryCode"/>
    <property name="PostalCodeLowerLimit" column="PostalCodeLowerLimit"/>
    <property name="PostalCodeUpperLimit" column="PostalCodeUpperLimit"/>
    <bag name="Parties" table="RoutingRule_Parties" lazy="false" cascade="save-update">
      <key column="RoutingRuleID"/>
      <many-to-many column="PartyId" class="FargoGateLib.Party, FargoGateLib" />
    </bag>          
    <bag name="DbConnectionEntries" table="RoutingRule_DbConnectionEntries" lazy="false" cascade="save-update">
      <key column="RoutingRuleID"/>
      <many-to-many column="DbConnectionEntryId" class="FargoGateLib.DbConnectionEntry, FargoGateLib" />
    </bag>          
    <property name="Ignore" column="Ignore"/>
  </class>          
</hibernate-mapping>

Please note that the bag element's type is set to "System.String".

Now this works fine! NHibernate creates the tables defined and all information is persisted. The problem is that I cannot figure out how to query this by joining the DestinationCountries-bag.

This is my attempt:

   IList<RoutingRule> routingRules = session.CreateCriteria(typeof(RoutingRule))
                       .Add(Restrictions.Eq("Ignore", false))
                       .Add(Restrictions.Eq("MessageType", MessageType.Booking))
                       .Add(Restrictions.Eq("TransportMethod", transportMethod))
                       .Add(Restrictions.Lt("PostalCodeLowerLimit", zipcode))
                       .Add(Restrictions.Gt("PostalCodeUpperLimit", zipcode))
                       .Add(Restrictions.Eq("PickupCountryCode", pickupCountry))
                       .SetFetchMode("DestinationCountryCodes", FetchMode.Join)
                       .CreateCriteria("DestinationCountryCodes")
                       .Add(Expression.Eq("CountryCode", destCountry))
                       .SetFetchMode("Parties", FetchMode.Eager)
                       .CreateCriteria("Parties")
                       .Add(Expression.Eq("Identifier", customerIdentifier))
                       .List<RoutingRule>(); 

It works fine with only the Parties-join, however, when I add the DestinationCountries-join then I get the following error message:

NHibernate.MappingException: collection was not an association: FargoGateLib.RoutingRule.DestinationCountryCodes

What gives!? I do not really know how to write the query so as to make this work.

Thanks in advance for any tips.