Is there an NHibernate criterion which does actually nothing?

Question

I'm looking for an NHibernate criterion which does not add a restriction to a criteria. The reason for this is that I have a method which converts some input parameters into a criterion which is added to a criteria. There is a constellation of the input parameters where no restriction needs to by applied. Therefore I want to return some kind of dummy criterion.

Is there something like that in NHibernate?

Best Regards,
Oliver Hanappi

Answer 1

well you could do something like Restrictions.IsNotNull("id") if querying against an entity with 'id' being a primary key (and so can never be null). Anything that evaluates to no logical restriction can be used based on your requirements.

Answer 2

You can use an empty Conjuction which is always true (it resolves to "1 = 1").

eg.

ICriterion conditionalCriteria = includeCriteria 
    ? Restrictions.Eq("someEntity.Field", variable)
    : (ICriterion) Restrictions.Conjuction();

var query = Session
    .CreateCriteria<SomeEntity>("someEntity")
    .Add(conditionalCriteria)
    .SetResultTransformer(Transformers.AliasToBean<SomeEntity>())
    .List<SomeEntity>();

Answer 3

You can add criteria as needed so just check your parameters for being null, if they are not null then add the criteria. See example:

Criteria cr = session.createCriteria(Employee.class)
cr.add(Restrictions.like("firstName", "Bob%"));

if (par_salary.IsNotNullOrEmpty())
{
     cr.add(Restrictions.eq("salary", par_salary));
}
List results = cr.list();

part of this taken from Hibernate Criteria Queries