Nhibernate join tables by multiple columns

Question

I have the following problem with an NHibernate query.

one table

LearnerDocuments :
    LearnerNumber
    CandidateNumber
    ....

other table

LearnerRegistration :
    LearnerId
    LearnerNumber
    ....

the last one

Learner : 
    LearnerId 
    LearnerName 
    ....

The relation between LearnerDocuments and and LearnerRegistration doesn't exist.

How can I write a query that gets all LearnerRegistration which have LearnerDocuments?

Answer 1

 criteria.CreateCriteria(typeof(LearnerRegistration), "av")
                    ......

                    .Add(Restrictions.IsNotNull("RegistrationNumber"))                    
                    .Add(Subqueries.PropertyIn("l.Id", detachedCriteria))

                 ;


            var candidate = DetachedCriteria.For<LearnerDocuments>("sd")
                        .SetProjection(Projections.ProjectionList()
                        .Add(Projections.Property("sd.CandidateNumber"))
                        .Add(Projections.Property("sd.RegistrationNumber")))
                        .Add(Restrictions.EqProperty("sd.CandidateNumber", "l.LearnerNumber") 
                        && Restrictions.EqProperty("sd.RegistrationNumber", "lr.RegistrationNumber")
                        );

            var proj = Projections.Conditional(Subqueries.Exists(candidate),Projections.Constant(true),Projections.Constant(false));