ICriteria and duplicate association path

jagid · **Joined:** Fri Jan 12, 2007 1:08 am **Posts:** 41

I need to flatten a relational structure. I am performing a projection based upon joined data. I've not included the projection below because it's not relevant to my question.

Using ICriteria I receive a "NHibernate.QueryException: duplicate association path: Parent.Child" exception with the following query:

Code:

ICriteria q = session.CreateCriteria(typeof(Parent), "p")
.CreateCriteria("p.Child", "c1", JoinType.LeftOuterJoin)
.Add(Expression.Eq("c1.Key", 'VALUE_1'))
.CreateCriteria("p.Child", "c2", JoinType.LeftOuterJoin)
.Add(Expression.Eq("c2.Key", 'VALUE_2');

However the equivalent IQuery is valid:

Code:

select from Parent p
left outer join p.Child c1
left outer join p.Child c2
where c1.Key = 'VALUE_1'
and c2.Key = 'VALUE_2'

Have I missed something? Is this a known problem?

karlchu · **Posted:** Thu Nov 15, 2007 11:05 am

This is probably more of a shortcoming of HQL rather than a feature. The HQL you gave should not be allowed; however, due to the implementation of the HQL parser, we are not catching all the invalid use cases. There is no concrete plan yet, mainly due to a lack of resources, to port over the H3 abstract-syntax-tree-based parser.

jagid · **Joined:** Fri Jan 12, 2007 1:08 am **Posts:** 41

If I understand correctly you are saying that a bug in HQL is allowing the syntax and that ICriteria is actually correct. I don't know what behavior NHibernate is supposed to allow but what I am trying to do should be allowed.

What's the status of the AST parser port? Do you need help? Obviously the answer is yes - what help do you need?

Actually the HQL doesn't give me the data that I want either. I want to generate the following SQL:

Code:

select  {...}
from    Parent p
        left outer join Child c1
          on p.ID = c1.ParentID
          and c1.Key = 'VALUE_1'
        left outer join Child c2
          on p.ID = c2.ParentID
          and c2.Key = 'VALUE_2'

but this is what NHibernate outputs:

Code:

select  {...}
from    Parent p
        left outer join Child c1
          on p.ID = c1.ParentID
        left outer join Child c2
          on p.ID = c2.ParentID
where   c1.Key = 'VALUE_1'
and     c2.Key = 'VALUE_2'

For now I'm going to fall back to ISQLQuery.

karlchu · **Posted:** Thu Nov 15, 2007 1:07 pm

You issue is perhaps similar to, if not the same as, this:
http://jira.nhibernate.org/browse/NH-514

jagid · **Joined:** Fri Jan 12, 2007 1:08 am **Posts:** 41

Yes, this is the same problem. From what I understand it's not worth attempting to fix this until the HQL parser rewrite is complete. Once again I am offering help with the rewrite.

karlchu · **Posted:** Thu Nov 15, 2007 2:44 pm

I think some effort has been put into it already. I believe translation of the grammar has been done; I can't recall exactly where it is at now. Please post a message on the NHibernate-Development mailing list. Perhaps something can be coordinated to get it going again. Thanks for your interest.