Question

I am looking for a way to build an OR operator into a query to look for a particular value in one field of a table as well as in another field of a joined table. This is pretty basic in SQL, but I can’t for the world figure out how to do this in NHibernate. I have been searching the web, but the examples I find are pretty nebulous to me and I find them hard to apply to my particular implementation.

I have an class called Party, with a string-field called reference, which is the main reference. New requirements demanded the option to also being able to add a lot of side-references to a party. So I had to add another class called PartyReference that has a many-to-one relationship to Party.

Now with a given reference I have to look its value up in both this main reference field as well as among the side references. But as long as I cannot figure out to say to NHibernate that EITHER this field must correspond to the value OR one of the others, I cannot make it work.

I have made a workaround that looks like this, but it is inelegant and stupid, as there has to be way to say “OR”:

   public Party GetPartyOnAnyReference(string reference)
       {
           Party party;

           ISession session = Factory.OpenSession();
           ITransaction tx = session.BeginTransaction();
           try
           {
               //first search on main reference
               ICriteria criteria1 = session.CreateCriteria(typeof(Party));
               criteria1.Add(Restrictions.Eq("Reference", reference));
               IList<Party> parties1 = criteria1.List<Party>();
               party = parties1.Count > 0 ? parties1[0] : null;

               //then try with side-references
               if (party == null)
               {
                   ICriteria criteria2 = session.CreateCriteria(typeof(Party));
                   criteria2
                           .SetFetchMode("References", FetchMode.Eager)
                           .CreateCriteria("References")
                           .Add(Expression.Eq("Reference", reference));
                   IList<Party> parties2 = criteria2.List<Party>();
                   party = parties2.Count > 0 ? parties2[0] : null;
               }

               session.Close();
           }
           catch (Exception e)
           {
               tx.Rollback();
               session.Close();

               if (e.GetType().ToString() == "NHibernate.ObjectNotFoundException")
                   party = null;
               else throw;
           }
           return party;
       }

I of course realize I can also solve this issue by simply removing the main reference from the Party class alltogether and treat it on par with the other references, as a PartyReference. But at some stage I will have to use an OR query with NHibernate anyway, so I might just as well solve it now with this particular case.

Any ideas?

Answer 1

You can use Restrictions.Or or use a Disjunction for multiple or’s.

session.CreateCriteria<Party>()
    .CreateAlias("References", "r", JoinType.LeftOuterJoin)
    .Add(Restrictions.Or(
        Restrictions.Eq("Reference", reference),
        Restrictions.Eq("r.Reference", reference)))
    .SetResultTransformer(new DistinctRootEntityResultTransformer())
    .List<Party>();