Nhibernate filtering by user defined function output

Question

I'm reasonably new to NHibernate and everything has been going pretty well so far but I've come across a problem I'm not exactly sure of how to go about solving. Basically I need to filter by the output of a User Defined function. If I was writing in SQL this is what I'd write:

declare @Latitude decimal
declare @Longitude decimal
declare @radius int

set @Latitude = -118.4104684 
set @Longitude = 34.1030032

select  * 
from    store
where   dbo.CalculateDistance([Latitude], [Longitude], @Latitude, @Longitude) < @radius

I've seen the formula attribute which I don't think is appropriate, named queries and examples of creating your own dialect extension (which seemed a little over kill). I would've thought there was a more straight forward way of doing it but I can't seem to find a tidy example.

Answer 1

You could use SQL expression in your hibernate queries. Assuming you've mapped a Store type you could write the following query:

var result = session
    .CreateCriteria<Store>()
    .Add(Expression.Sql(
        "dbo.CalculateDistance({alias}.Latitude, {alias}.Longitude, ?, ?) < ?",
        new object[] { 
            -118.4104684d, 
            34.1030032d, 
            100 
        },
        new IType[] { 
            NHibernateUtil.Double, 
            NHibernateUtil.Double, 
            NHibernateUtil.Int32 
        }
    ))
    .List<Store>();

Answer 2

Creating custom dialect extensions is rather easy:

public class CustomFunctionsMsSql2005Dialect : MsSql2005Dialect 
{ 
   public CustomFunctionsMsSql2005Dialect() 
   { 
      RegisterFunction("calculatedistance",
                       new SQLFunctionTemplate(NHibernateUtil.Int32,
                                               "CalculateDistance(?1, ?2, ?3, ?4)"));
   }
}

Register it, like so:

<property name="hibernate.dialect">
  CustomFunctionsMsSql2005Dialect, MyAssembly
</property>

Now you can use it like any other HQL function in queries like those created with session.CreateQuery().