check if node exists

Question

i want to check if an element exists and manipulate this element if it does, eg...

 

XmlNode node = ....

if (node.selectnodes("whatever") exists)

then...

do something

 

thanks if you can help.

Answer 1

You can do this on several ways. You can walktrough all nodes with a XmlTextReader and look for a specific Xml Node Name.

You can XPath as well. This is a simple query language for Xml, for more information about it look here.

Here is a little example that select a specified XmlNode:

using System; using System.IO; using System.Xml; public class Sample {   public static void Main()   {       XmlDocument doc = new XmlDocument();       doc.Load("booksort.xml");       //Select the book node with the matching attribute value.       XmlNode nodeToFind;       XmlElement root = doc.DocumentElement;       // Selects all the title elements that have an attribute named lang       nodeToFind = root.SelectSingleNode("//title[@lang]");       if( nodeToFind != null )       {            // It was found, manipulate it.       }       else      {            // It was not found.       }   } }

Answer 2

thankyou!!

 

does the same thing work with attributes

 

eg.

if(node.Attributes["attributes"] != null)

...

Answer 3

Attributes can be selected using XPath expressions via SelectNodes and SelectSingleNodes, just prefix the attribute name with the path expression '@'.  See http://msdn.microsoft.com/library/en-us/xmlsdk/html/daa75346-ccd1-4033-9250-9b9f3ba5762c.asp

Answer 4

This can also be achieved through:
'' DETERMINE IF THE xml contains the older variable name or the newer correct variable name "Of" versus "of".

 

                        If locXmlNodes(0).Item("Dude") Is Nothing Then
                            Response.Write("Dude does not exist")
                        Else
                            Response.Write("Dude does exist")
                        End If

Other things I started to find helpful with xpath are as follows too:

            locXmlNodes = reqXmlDoc.SelectNodes("//TraineeHistory/Person/PersonHistory/PersonTraining/Course/CourseCode[contains(.,'S') and substring-after(.,'')]/../DateofTraining[contains(.,'2009') and substring-after(.,'')]/..")
            Response.Write("NUMBER OF PARENT NODES in houston data is with CourseCode='*S*' and DateofTraining='2009' is:" + locXmlNodes.Count.ToString() + "<Br>")
            'Response.Write(locXmlNodes("CourseCode").Value.ToString())
            Response.Write(locXmlNodes(0).InnerXml.ToString())
            'Response.Write(locXmlNodes(0).Item("CourseCode").Value.ToString())
            Response.Write("<br/>" + locXmlNodes(0).HasChildNodes.ToString())
            Response.Write("<br/>" + locXmlNodes(0).ChildNodes.Count.ToString())
            Response.Write("<br/>" + locXmlNodes(0).FirstChild.ToString())
            Response.Write("<br/>" + locXmlNodes(0).FirstChild.InnerXml.ToString())
            Response.Write("<br/>" + locXmlNodes(0).Item("CourseCode").InnerXml.ToString())
            Response.Write("<br/>" + locXmlNodes(0).Item("CourseName").InnerXml.ToString())
            Response.Write("<br/>" + locXmlNodes(0).Item("DateOfExpiration").InnerXml.ToString())
            Response.Write("<br/>" + locXmlNodes(0).Item("DateofTraining").InnerXml.ToString())
            Response.Write("<br/>" + locXmlNodes(0).Item("TrainingType").InnerXml.ToString())

            Response.Write("<br/>")
            locXmlNodes = reqXmlDoc.SelectNodes("//TraineeHistory/Person/PersonHistory/PersonTraining/Course/TrainingType[.='BASIC' or .='BASICREF'  or .='CONFINED']/..")
            Response.Write("[c]NUMBER OF NODES in houston data is with TrainingType='BASIC' or TrainingType='BASICREF' or TraniningType='CONFINED' is:" + locXmlNodes.Count.ToString() + "<BR>")

            '======================================
            ' format of date needs to be 10/01/2009  it can not be 10/1/09; it can not be 1/1/09; it has to have 10 characters to work
            ' we will then do a integer comparison for the yyyymm value  since you can ot compare dates in XPATH natively
            ' SEARCH REFERENCE: asp.net xpath compare dates in xml nodes or atributes
            '======================================
            strXPathQuery = "(substring(.,7,4)*100)+substring(.,1,2) >= " + todayYearMonth.ToString()
            Response.Write("<br/>")
            locXmlNodes = reqXmlDoc.SelectNodes("//TraineeHistory/Person/PersonHistory/PersonTraining/Course/TrainingType[.='BASIC' or .='BASICREF'  or .='CONFINED']/../DateOfExpiration[" + strXPathQuery + "]/..")
            Response.Write("[c]NUMBER OF NODES in houston data is with TrainingType='BASIC' or TrainingType='BASICREF' or TraniningType='CONFINED' And DateOfExpiration >= " + todayYearMonth.ToString() + " is:" + locXmlNodes.Count.ToString() + "<BR>")
            If locXmlNodes.Count >= 1 Then
                If locXmlNodes(0).HasChildNodes Then
                    For listCnt = 0 To locXmlNodes.Count - 1
                        Response.Write("(" + listCnt.ToString() + ")CourseCode=" + locXmlNodes(listCnt).Item("CourseCode").InnerXml.ToString() + "<BR/>")
                        Response.Write("(" + listCnt.ToString() + ")CourseName=" + locXmlNodes(listCnt).Item("CourseName").InnerXml.ToString() + "<BR/>")
                        Response.Write("(" + listCnt.ToString() + ")DateOfExpiration=" + locXmlNodes(listCnt).Item("DateOfExpiration").InnerXml.ToString() + "<BR/>")
                        If locXmlNodes(listCnt).Item("DateofTraining") Is Nothing Then
                            Response.Write("(" + listCnt.ToString() + ")***DateOfTraining=" + locXmlNodes(listCnt).Item("DateOfTraining").InnerXml.ToString() + "<BR/>")
                        Else
                            Response.Write("(" + listCnt.ToString() + ")DateofTraining=" + locXmlNodes(listCnt).Item("DateofTraining").InnerXml.ToString() + "<BR/>")
                        End If
                        If Not (locXmlNodes(0).Item("TrainingType") Is Nothing) Then
                            Response.Write("(" + listCnt.ToString() + ")TrainingType=" + locXmlNodes(listCnt).Item("TrainingType").InnerXml.ToString() + "<BR/>")
                        End If
                        Response.Write("========== SAVE TO THE DATABASE")
                        Response.Write("<br>")
                    Next
                End If
            End If

GREATE WEBSITE REFERENCES I FOUND WERE AS FOLLOWS:
http://bytes.com/topic/visual-basic-net/answers/372556-xpath-query-multiple-parameters
http://www.eggheadcafe.com/articles/20030627d.asp

asp.net best way to query and save xml data to sql database
http://stackoverflow.com/questions/61233/the-best-way-to-shred-xml-data-into-sql-server-database-columns
http://stackoverflow.com/questions/667168/best-method-to-populate-xml-from-sql-query-in-asp-net

search:asp.net xpath compared to linqtoxml  (SOUNDS TO ME XPATH STILL IS A GOOD METHOD FOR QUERyiNG XML DATA)
http://smartdev.wordpress.com/2009/04/15/xpath-vs-linq-to-xml/
http://blog.dreamlabsolutions.com/post/2008/12/04/LINQ-to-XML-and-LINQ-to-XML-with-XPath-performance-review.aspx

search:
http://forums.asp.net/p/1072271/1569035.aspx
http://forums.asp.net/t/1123338.aspx
http://forums.asp.net/p/1399792/3023829.aspx

IMPORTANT THOUGHT ....WE HAVE TO GET THE PARENT
http://bytes.com/topic/visual-basic-net/answers/372556-xpath-query-multiple-parameters


Thanks,

Doug Lubey of Louisiana
www.douglubey.com

Answer 5

Hi

 

SelectSingleNode is not working for me in VBScript. if the node does not exist.

 

Set objFamAttrXML = CreateObject("Microsoft.XMLDOM")

objFamAttrXML.Async = "false"

objFamAttrXML.SetProperty "SelectionLanguage", "XPath"

objFamAttrXML.validateOnParse = False

objFamAttrXML.resolveExternals = False

objFamAttrXML.Load (MY_QC & "\\Family_Attr.XML")

logW ADD,DBG, "XML File : " & MY_QC & "\Family_Attr.XML"

 

set famNode = Nothing

famNode = objFamAttrXML.SelectSingleNode("/familyattr/family[@attr='" & CIFamily & "']")

 

If Not IsObject(famNode) then

logW ADD, ERROR, "Family does not exist in "  & MY_QC & "\Family_Attr.XML"

bPASS = false

myRC = -1

Exit Sub

End if

 

 

The If is never executed and script breaks after selectsinglenode statment.

---

Anubhav

Answer 6

Consider to start a new thread with your own topic, then please provide a sample of the XML you are running that VBScript code against and tell us exactly which error message you get. If you want us to understand your problem then it is best to post enough code to allow us to easily reproduce the problem so show all variable declarations and initializations.

In general I would suggest the following code changes:

1. Instead of objFamAttrXML.Async = "false" use objFamAttrXML.Async = False
2. Check the result of calling the load method e.g.

  If objFamAttrXML.Load (MY_QC & "\\Family_Attr.XML") Then

    ' now here you can access nodes

  Else

    'check or output objFamAttrXML.parseError.reason

  End If

I also think instead of

  If Not IsObject(famNode) then

You rather need

  If famNode Is Nothing Then

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