How do I update an XML attribute from an MSBuild script?

Question

I am using MSBuild and MSBuild Community Tasks (using XMLUpdate and XMLMassUpdate) to update various sections of my Web.config one thing has me stumped though. If I have:

<configuration>
    <nlog throwExceptions="true" xmlns="http://www.nlog-project.org/schemas/NLog.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
       <targets>
            <target name="file" xsi:type="File" fileName="${logDirectory}\SomeLog.log" layout="${message}"/>
        </targets>
    </nlog> 
</configuration>

and I try to replace the fileName of the target

<XmlUpdate XmlFileName="$(BuildDir)\Builds\%(Configuration.Identity)\_PublishedWebsites\Presentation\Web.config"
           XPath="//configuration/nlog/targets/target[@fileName]"
           Value="${logDirectory}\SomeLog_%(Configuration.Identity).log" />

It reports as being unable to find anything to update, so my question is how can I get the filename attribute to updated?

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EDIT: Could this be a case of namespace clashes as the NLog section defines its own namespace?

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UPDATE: The posted answer declaring the name space does not work.

Answer 1

The first problem is the xpath is incorrect for updating the attribute, it is currently looking for "target" nodes with an attribute called "fileName" rather than the "fileName" attribute of the a node called "target".

The xpath you want is: /configuration/nlog/targets/target/@fileName

As for the namespace issue, Preet Sangha has the correct answer for that, you need to use the namespace prefix, and this must be applied to every sub-element as well, since they are all in that namespace.

The final statement being:

<XmlUpdate
  Prefix="n"
  Namespace="http://www.nlog-project.org/schemas/NLog.xsd"
  XmlFileName="output.xml"
  XPath="//configuration/n:nlog/n:targets/n:target/@fileName"
  Value="${logDirectory}\UpdateWorked.log" />