.SelectSingleNode in Powershell script using xPath not working on extracting values from web.config file

Question

Okay, so here is the snippet of my web.config file:

<?xml version="1.0" encoding="utf-8"?>
<configuration xmlns="http://schemas.microsoft.com/.NetConfiguration/v2.0">
<location path="." inheritInChildApplications="false">
<connectionStrings>
...
</connectionStrings>
</location>
<location path="." inheritInChildApplications="false">
<appSettings>
<!--IT Ops-->
<add key="SomeOtherKey" value="SomeOtherValue" />
<add key="SiteDomain" value="somedomain.com" />
<add key="SomeOtherKey" value="SomeOtherValue" />
....
</appSettings>
</location>
</configuration>

What I'm trying to do is find the node using xPath via Powershell. A couple things to note about this XML file:

there are multiple:

<location path="." inheritInChildApplications="false"> 

values in the xml file. They surround other nodes like etc...

I can find and replace the connection string values successfully using this script

$WebConfigFile = Join-Path $destination Web.config
[xml]$WebConfigXml = Get-Content ($WebConfigFile)
$WebConfigXml.configuration.location[2].connectionStrings.add | % { $_.connectionString = $_.connectionString -replace "some value", $sqlServerName }

But when I go to replace the add key="SiteDomain" value using this script:

$node = $WebConfigXml.configuration.location[3].appSettings.SelectSingleNode("add[@key = 'SiteDomain']")
$node.value = "someValue"
$WebConfigXml.Save($WebConfigFile)

it does not work. The $node value in this case contains an empty string.

I'm also trying just to read the node like this:

$appSettingsSection = $WebConfigXml.configuration.location[3].appSettings;
$existingSiteDomain = $appSettingsSection.SelectSingleNode("add[@key='SiteDomain']")

And I'm still getting an empty string for the $existingSiteDomain value.

I've looked at samples using SelectSingleNode and I can't quite seem to figure it out. Not too sure what I'm doing wrong.

Thanks, Mike

Answer 1

Your XML file has a namespace:

<configuration xmlns="http://schemas.microsoft.com/.NetConfiguration/v2.0">

so you need a namespace manager for SelectSingleNode (see section "Remarks"):

XPath expressions can include namespaces. Namespace resolution is supported using the XmlNamespaceManager. If the XPath expression includes a prefix, the prefix and namespace URI pair must be added to the XmlNamespaceManager.

Something like this should work:

$ns = New-Object System.Xml.XmlNamespaceManager($WebConfigXml.NameTable)
$ns.AddNamespace("ns", $WebConfigXml.DocumentElement.NamespaceURI)
$node = $WebConfigXml.SelectSingleNode("//ns:add[@key='SiteDomain']", $ns)