title: The method or operation is not implemented while using linq to nhibernate
body: <p>i m trying to use linq to nhibernate 3  and i have made following linq query</p>
  
  <pre><code> var a = (from c in Session.Query&lt;ChoiceValue&gt;()
                   join Specific in
                       (
                           (from choicevaluelocale in Session.Query&lt;ChoiceValueLocale&gt;()
                            where
                              choicevaluelocale.UICulture == "en-GB"
                            select new
                            {
                                choicevaluelocale.ChoiceValue.ChoiceGroup.ChoiceGroupName,
                                choicevaluelocale.ChoiceValue.ChoiceValueId,
                                choicevaluelocale.DisplayName,
                                choicevaluelocale.Description
                            }))
                         on new { c.ChoiceGroup.ChoiceGroupName, c.ChoiceValueId }
                     equals new { Specific.ChoiceGroupName, ChoiceValueId = (Int32)Specific.ChoiceValueId } into Specific_join
                   from Specific in Specific_join.DefaultIfEmpty()
                   select new
                   {
                       c.ChoiceGroup.ChoiceGroupName,
                       ChoiceValueId = (Int32?)c.ChoiceValueId,
                       SpecificValueDisplayName = Specific.DisplayName,
                       SpecificValueDescription = Specific.Description,
  
                   }).ToList();
  </code></pre>
  
  <p>but while executing it on n-hibernate in c# i got following error</p>
  
  <pre><code>The method or operation is not implemented
  </code></pre>
  
  <p>stack trace is</p>
  
  <pre><code>   at NHibernate.Linq.Visitors.QueryModelVisitor.VisitGroupJoinClause(GroupJoinClause
     groupJoinClause, QueryModel queryModel, Int32 index)
     at Remotion.Data.Linq.Clauses.GroupJoinClause.Accept(IQueryModelVisitor visitor, 
     QueryModel queryModel, Int32 index)
     at Remotion.Data.Linq.QueryModelVisitorBase.VisitBodyClauses(ObservableCollection`1  
     bodyClauses, QueryModel queryModel)
     at Remotion.Data.Linq.QueryModelVisitorBase.VisitQueryModel(QueryModel queryModel)
     at NHibernate.Linq.Visitors.QueryModelVisitor.GenerateHqlQuery(QueryModel  
     queryModel, VisitorParameters parameters, Boolean root)
     at NHibernate.Linq.NhLinqExpression.Translate(ISessionFactoryImplementor   
     sessionFactory)
  </code></pre>
  
  <p>can any one please help me to overcome this problem?</p>