Best way to get the value of one particular node of an XML string

14 Apr 2005 2:28 PM

Scott M. Lyon

I'm trying to figure out the best way (considering there could be instances
where I get a lot of data in this XML, and I want to minimize any slowdowns)
to extract the value of one particular node from an XML string (not saved as
a file, but passed as a string from another module).

For example, let's assume I get back XML in a string that looks like this:

<Commands>
    <cmd name="1">
        <item name="result">Complete</item>
    </cmd>
    <cmd name="2">
        <item name="result">Returned</item>
        <item name="id">12345</item>
    </cmd>
    <cmd name="3">
        <item name="result">Tested</item>
    </cmd>
</Commands>

I need an efficient way that I can (for example) return the value from the
cmd tag with name attribute "2", and then the item tag below that with the
name attribute "result" (in other words, for this case giving the string
"Returned".

What is going to be the best way to do this? It was suggested (here) that I
use the XmlTextReader, but I'm not totally sure how that would work.

Can anyone help?

Ideally I'd like a function (VB.NET) that takes the xml as one parameter (as
a string), and the cmd "name" as another parameter (also as a string), and
the item "name" as the third parameter, and returns a string containing the
value.

Thanks!
-Scott

14 Apr 2005 4:39 PM

Chris

Scott M. Lyon wrote:
Show quoteHide quote

> I'm trying to figure out the best way (considering there could be instances
> where I get a lot of data in this XML, and I want to minimize any slowdowns)
> to extract the value of one particular node from an XML string (not saved as
> a file, but passed as a string from another module).
>
>
> For example, let's assume I get back XML in a string that looks like this:
>
> <Commands>
>     <cmd name="1">
>         <item name="result">Complete</item>
>     </cmd>
>     <cmd name="2">
>         <item name="result">Returned</item>
>         <item name="id">12345</item>
>     </cmd>
>     <cmd name="3">
>         <item name="result">Tested</item>
>     </cmd>
> </Commands>
>
>
> I need an efficient way that I can (for example) return the value from the
> cmd tag with name attribute "2", and then the item tag below that with the
> name attribute "result" (in other words, for this case giving the string
> "Returned".
>
>
> What is going to be the best way to do this? It was suggested (here) that I
> use the XmlTextReader, but I'm not totally sure how that would work.
>
>
> Can anyone help?
>
>
> Ideally I'd like a function (VB.NET) that takes the xml as one parameter (as
> a string), and the cmd "name" as another parameter (also as a string), and
> the item "name" as the third parameter, and returns a string containing the
> value.
>
>
> Thanks!
> -Scott
>
>

You can do what you want using XmlDocument.SelectNodes or
XmlDocument.SelectSingNode.

You need to know XPath to do what you want but there is good help and
examples if you look under "XPath [MS XML], examples". I think the path
you need (and I warn you I'm not well practiced in xpath) is 'cmd[@name
= "3"' That says give me all the nodes who name is cmd and has an
attribute of name that equals 3.

Good luck.
Chris

14 Apr 2005 5:00 PM

jpontani

Function GetVal(ByVal xml As String, ByVal cmdname As String, ByVal cmditem
As String) As String
    Dim myDoc As New Xml.XmlDocument
    myDoc.LoadXml(xml)
    For Each Node As Xml.XmlNode In myDoc.FirstChild.ChildNodes
        For Each a As Xml.XmlAttribute In Node.Attributes
            If (a.Value = cmdname) Then
                For Each cNode As Xml.XmlNode In Node.ChildNodes
                    For Each ca As Xml.XmlAttribute In cNode.Attributes
                        If (ca.Value = cmditem) Then
                            GetVal = cNode.InnerText
                        End If
                    Next
                Next
            End If
        Next
    Next
End Function

Chris's method is definitely cleaner, but might take some time to learn
XPath and it's syntax. Above is a function that will return the text of the
node that is under cmd with name cmdname, and the node that has the name
cmditem.

GetVal(xmlhere, "2", "result") returns "Returned", and GetVal(xmlhere, "2",
"id") returns "12345"

--
Damian

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