NHibernate: IUserType not working - nhibernate

Question

I have this class that implements IUserType:
public class StringToIntType : IUserType
{
/// <summary>
/// mutable object = an object whose state CAN be modified after it is created
/// </summary>
public bool IsMutable
{
get { return false; }
}
public Type ReturnedType
{
get { return typeof(StringToIntType); }
}
public SqlType[] SqlTypes
{
get { return new[] { NHibernateUtil.String.SqlType }; }
}
public object NullSafeGet(IDataReader rs, string[] names, object owner)
{
var obj = NHibernateUtil.String.NullSafeGet(rs, names[0]);
if (obj == null) return null;
var s = (string)obj;
int i;
if (Int32.TryParse(s, out i))
return i;
return -1;
}
public void NullSafeSet(IDbCommand cmd, object value, int index)
{
if (value == null)
{
((IDataParameter)cmd.Parameters[index]).Value = DBNull.Value;
}
else
{
var i = (int)value;
((IDataParameter)cmd.Parameters[index]).Value = i.ToString();
}
}
public object DeepCopy(object value)
{
return value;
}
public object Replace(object original, object target, object owner)
{
return original;
}
public object Assemble(object cached, object owner)
{
return cached;
}
public object Disassemble(object value)
{
return value;
}
public new bool Equals(object x, object y)
{
if (ReferenceEquals(x, y)) return true;
if (x == null || y == null) return false;
return x.Equals(y);
}
public int GetHashCode(object x)
{
return x == null ? typeof(int).GetHashCode() + 473 : x.GetHashCode();
}
}
My mapping:
public BarausLangMap()
{
Table("BARAUSLANG");
Id(x => x.ula).CustomType<StringToIntType>();
Map(x => x.bezeichnung);
Map(x => x.sprache);
Map(x => x.la);
Where("la = 'SPE'");
}
My properties:
public virtual int ula { get; set; }
public virtual String bezeichnung { get; set; }
public virtual Int32? sprache { get; set; }
public virtual String la { get; set; }
Problem: When I do
var b = session.Get<BarausLang>(5);
It says
{NHibernate.TypeMismatchException: Provided id of the wrong type.
Expected: MobileServiceServer.Models.StringToIntType, got System.Int32
What is the problem? I thought nHibernate would call StringToIntType implicitely to convert from int to string and vice versa. I think that is the whole point. I thought StringToIntType was only for the mapping? How should I use it then?

Answer 1

You are correct, ReturnedType should return the type that NullSafeGet will return. The example code you linked to is incorrect, ReturnedType should return typeof(bool).
Also, getting the Equals method right is very important and I recommend a small change to your code:
public new bool Equals(object x, object y)
{
if (ReferenceEquals(x, y)) return true;
var xString = x as string;
var yString = y as string;
if (xString == null || yString == null) return false;
return xString.Equals(yString);
}

Answer 2

I MAY have found the problem:
public Type ReturnedType
above returns StringToIntType, and i THINK it should be int.
However, on:
http://lostechies.com/rayhouston/2008/03/23/mapping-strings-to-booleans-using-nhibernate-s-iusertype/
the method returns the type that implements IUserType.
Please confirm.