use nhibernate ResultTransformer - nhibernate

Question

I am using Nhibernate last version in my MVC project
I want to make a query on an object type names "Person" but person has many properties. In one of my queries I'd better not to have most of these properties.
Here is Person:
public partial class Person
{
virtual public User User { get; set; }
virtual public string FirstName { get; set; }
virtual public string LastName { get; set; }
virtual public int Gender { get; set; }
virtual public Contact Contact { get; set; }
virtual public BirthCertificate PersonBirthCertificate { get; set; }
}
In the query I just want first name and last name of the person.
So I decided to use ResultTransformer and implement it like this:
public class PersonResultTransformer : IResultTransformer
{
private Type result;
private PropertyInfo[] properties;
#region IResultTransformer Members
public IList TransformList(IList collection)
{
return collection;
}
public PersonResultTransformer (Type result, params string[] names)
{
this.result = result;
List<PropertyInfo> props = new List<PropertyInfo>();
foreach (string name in names)
{
props.Add(result.GetProperty(name));
}
properties = props.ToArray();
}
public object TransformTuple(object[] tuple, string[] aliases)
{
object instance = Activator.CreateInstance(result);
for (int i = 0; i < tuple.Length; i++)
{
var t = properties[i].Name;
var value = tuple[i].GetType().GetProperty(t).GetValue(tuple[i], null);
instance.GetType().GetProperty(t).SetValue(instance, value, null);
}
return instance;
}
#endregion
}
and for getting want I want with linq query :
var person = Repository<Person>.Find(p => p.LastName.Equals("Nadal")
, new PersonResultTransformer (typeof(Person), "FirstName", "LastName"));
////////////////
public IQueryable<T> Find(Expression<Func<T, bool>> expression, IResultTransformer transformer)
{
return Session.CreateCriteria<T>().SetResultTransformer(transformer).List<T>()
.AsQueryable().Where(expression);
}
Is it OK? can it be more customized? do I use it correctly?
It seems that it has a big problem: it gets all persons's first name and last name and then select from them, those having last name="nadal", and the performance is not good at all

Answer 1

first you have to delegate to a query which understands expressions
using NHibernate.Linq;
public IQueryable<T> Find(Expression<Func<T, bool>> expression)
{
return Session.Query<T>().Where(expression);
}
then you can
var personDTOs = Repository<Person>.Find(p => p.LastName.Equals("Nadal"))
.Select(person => new { person.FirstName, person.LastName });
you can shorten the resulttransformer a lot, but you cant use it with Linq2NHibernate.
public class PersonResultTransformer : IResultTransformer
{
private Type result;
private List<PropertyInfo> properties = new List<PropertyInfo>();
public IList TransformList(IList collection)
{
return collection;
}
public PersonResultTransformer (Type result, params string[] names)
{
this.result = result;
foreach (string name in names)
{
properties.Add(result.GetProperty(name));
}
}
public object TransformTuple(object[] tuple, string[] aliases)
{
object instance = Activator.CreateInstance(result);
for (int i = 0; i < tuple.Length; i++)
{
properties[i].SetValue(instance, tuple[i], null);
}
return instance;
}
}

Answer 2

You use Session.CreateCriteria<T>() but you do not add any criteria to it. So, the query is executed without criteria and then transformed and filtered.
You have to find a way to add your specifications to the Find method in a way that Nhibernate's ICriteria can handle, or use Linq to Nhibernate (beware of some issues though!).

Answer 3

I could be wrong - but I think you're overdoing this.
You could more easily utilize lazy loading to not fetch the properties you don't need.