public class XmlDocumentUserType : UserTypeBase
{
   public XmlDocumentUserType()
   {
   }

   #region UserTypeBase Members
   public override object NullSafeGet(IDataReader rs, string[] names, object owner)
   {
      object xmlDocument = rs[names[0]];
      if(xmlDocument == null || !(xmlDocument is string))
         return new XmlDocument();
      
      string xml = xmlDocument as string;
      XmlDocument effectiveXmlDocument = new XmlDocument();
      effectiveXmlDocument.LoadXml(xml);
      
      return effectiveXmlDocument;
   }

   public override void NullSafeSet(IDbCommand cmd, object value, int index)
   {
      XmlDocument xmlDocument = value as XmlDocument;
      (cmd.Parameters[index] as IDataParameter).Value = xmlDocument.InnerXml;
   }

   public override object DeepCopy(object value)
   {
      return (value as XmlDocument).Clone() as XmlDocument;
   }

   public override SqlType[] SqlTypes
   {
      get { return new SqlType[] { new StringClobSqlType() }; }
   }

   public override Type ReturnedType
   {
      get { return typeof(XmlDocument); }
   }
   #endregion
}

public abstract class UserTypeBase : IUserType
{
   public UserTypeBase()
   {
   }

   #region IUserTypeMembers
   public abstract object NullSafeGet(IDataReader rs, string[] names, object owner);

   public abstract void NullSafeSet(IDbCommand cmd, object value, int index);

   public abstract object DeepCopy(object value);

   public abstract SqlType[] SqlTypes
   { get; }

   public abstract Type ReturnedType
   { get; }

   public virtual bool IsMutable
   {
      get { return false; }
   }

   public virtual new bool Equals(object x, object y)
   {
      if(x != null)
         return x.Equals(y);

      return y == null;
   }
   #endregion
}