NHibernate Merge problem with XMLType

I have a class that contains a property of type XmlElement. The property is mapped as following:

<property name="XamlForm" column="XamlForm" type="KTN.Base.Data.Types.XmlType, KTN.Base.Data" />

The XmlType class:

[Serializable]
public class XmlType : IUserType
{
    public new bool Equals(object x, object y)
    {
        XmlElement xdoc_x = (XmlElement)x;
        XmlElement xdoc_y = (XmlElement)y;

        if (xdoc_x == null && xdoc_y == null) return true;

        if (xdoc_x == null || xdoc_y == null) return false;

        return xdoc_y.OuterXml == xdoc_x.OuterXml;
    }

    public object NullSafeGet(IDataReader rs, string[] names, object owner)
    {
        if (names.Length != 1)
            throw new InvalidOperationException("names array has more than one element. can't handle this!");
        XmlDocument document = new XmlDocument();
        string val = rs[names[0]] as string;
        if (val != null)
        {
            document.LoadXml(val);

            return document.DocumentElement;
        }
        return null;
    }

    public void NullSafeSet(IDbCommand cmd, object value, int index)
    {
        DbParameter parameter = (DbParameter)cmd.Parameters[index];
        if (value == null)
        {
            parameter.Value = DBNull.Value;
            return;
        }
        parameter.Value = ((XmlElement)value).OuterXml;
    }

    public object DeepCopy(object value)
    {
        if (value == null) return null;
        XmlElement other = (XmlElement)value;
        XmlDocument xdoc = new XmlDocument();
        xdoc.LoadXml(other.OuterXml);
        return xdoc.DocumentElement; /**/
    }

    public SqlType[] SqlTypes
    {
        get
        {
    开发者_开发问答        return new SqlType[] { new SqlXmlType() };
        }
    }

    public System.Type ReturnedType
    {
        get { return typeof(XmlDocument); }
    }

    public bool IsMutable
    {
        get { return true; }
    }

    public object Assemble(object cached, object owner)
    {
        return cached;
    }

    public object Disassemble(object value)
    {
        return value;
    }

    public int GetHashCode(object x)
    {
        return x.GetHashCode();
    }

    public object Replace(object original, object target, object owner)
    {
        // Changed return original to return target... 
        return target;
    }

}

After invoke the function Merge from NHibernate, this property is null. Any Idea? Thanks in advance

NHibernate 3 has out of the box types for both XDocument and XmlDocument.

You shouldn't need to roll your own.