XPath Queries Using XmlDocument and SelectSingleNode

public sealed class ProjectSpecific
    {
        public static string GetErrorMessageById(int nMessageID)
        {
            XmlDocument xmlErrorMessages = GetXMLErrorMessagesDocument();
            return xmlErrorMessages.DocumentElement.SelectSingleNode("message[id=" + nMessageID.ToString() + @"]").FirstChild.NextSibling.InnerText;
        }
        public static string GetErrorMessageByFieldId(string strFieldID)
        {
            XmlDocument xmlErrorMessages = GetXMLErrorMessagesDocument();
            return xmlErrorMessages.DocumentElement.SelectSingleNode("message[field_id=" + strFieldID + @"]").FirstChild.NextSibling.InnerText;
        }
 
        private static XmlDocument GetXMLErrorMessagesDocument()
        {
            XmlDocument xmlErrorMessages = new XmlDocument();
 
            if (HttpContext.Current.Cache["ErrorMsg_XML"] != null)
                xmlErrorMessages = (XmlDocument)HttpContext.Current.Cache["ErrorMsg_XML"];
            else
            {
                xmlErrorMessages.Load(HttpContext.Current.Server.MapPath("~/includes/xml/ErrorMessageCopy.xml"));
                HttpContext.Current.Cache["ErrorMsg_XML"] = xmlErrorMessages;
            }
            return xmlErrorMessages;
        }
    }
 
______________________________________________________________
 
 
string str1 = Utils.ProjectSpecific.GetErrorMessageById(1);
 
string str2 = Utils.ProjectSpecific.GetErrorMessageByFieldId("tbForename");
 
<?xml version="1.0" encoding="utf-8" ?>
 
<messages>
  <message>
    <id>0</id>
    <text>You must supply your forename</text>
    <fieldid>tbForename</fieldid>
  </message>
  <message>
    <id>1</id>
    <text>You must supply your surname</text>
    <field_id>tbSurname</field_id>
  </message>
  <message>
    <id>2</id>
    <text>You must supply your home address</text>
    <field_id>tbHomeAddress</field_id>
  </message>
  <message>
    <id>3</id>
    <text>You must supply your mobile number</text>
    <field_id>tbMobileNumber</field_id>
  </message>
  <message>
    <id>4</id>
    <text>You must supply a valid email address</text>
    <field_id>tbEmailAddress</field_id>
  </message>
</messages>

                                  

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