I am creating a method that can create filter understood by NHibernate (by filter i mean a set of ICriteria object for example) from my abstract filter object.

public static IEnumerable<ICriterion> ToNhCriteria(this MyCriteria criteria)
{
   // T4 generated function
   // lots of result.Add(Expression.Or(Expression.Eq(),Expression.Eq)) expression trees - hard to generate
   // Is there a way to generate HQL/Linq query here istead?
}

then i want to do something like

session.CreateCriteria<Entity>().Add(myCriteria.ToNhCriteria())

to filter entities. The problem is that using Expression. methods (Expression.Or etc) is quite tedious (the method is generated and i have multiple or statements that have to be joined into an expression somehow). Is there a way to avoid using Expression.Or() and create ICrietrion / ICriteria using LINQ or HQL?