Load XML containing custom namespace

Question

Using PowerShell scripts to dynamically append XML tags. In this case trying to add a custom ElasticSearch target for NLog (from here).

$source = '<target name="elastic" xsi:type="BufferingWrapper">  </target>'

When converting $source to XML using

[xml]$source

or

$xml = New-Object -TypeName System.Xml.XmlDocument
$xml.LoadXml($source)

I get the following error

Cannot convert value "<targetname="elastic" xsi:type="BufferingWrapper"> </target>" to type "System.Xml.XmlDocument". Error: "'xsi' is an undeclared prefix."

Any suggestions?

Almost, but not quite there:

I can use ConvertTo-Xml $source -as Document but the result doesn't use the <target> tag, it uses <Object>, which doesn't work in this case.

<?xml version="1.0" encoding="utf-8"?>
<Objects>
  <Object Type="System.String">&lt;target name="elastic" xsi:type="BufferingWrapper"
<Objects>

Community · Accepted Answer · 2017-05-23 12:19:17Z

You could load the XML fragment as described in this answer:

$source = '<target name="elastic" xsi:type="BufferingWrapper"></target>'
$sreader = New-Object IO.StringReader $source
$xreader = New-Object Xml.XmlTextReader $sreader
$xreader.Namespaces = $false
$fragment = New-Object Xml.XmlDocument
$fragment.Load($xreader)

However, assuming that you want to import that fragment into another XML data structure at some point, doing so will probably lead to other problems (see for instance this question).

To work around this issue add a dummy root node with the proper namespace definition to your XML fragment:

$source = '<target name="elastic" xsi:type="BufferingWrapper">  </target>'
[xml]$fragment = "<dummy xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance'>$source</dummy>"

That way you can import the node into another XML document like this (provided the other XML file also contains the proper namespace definition):

[xml]$xml = Get-Content 'C:\path\to\master.xml'

$nsm = New-Object Xml.XmlNamespaceManager $xml.NameTable
$nsm.AddNamespace('xsi', $xml.NamespaceURI)

$node = $xml.ImportNode($fragment.DocumentElement.target, $true)

$targets = $xml.SelectSingleNode('//targets', $nsm)
$targets.AppendChild($node) | Out-Null

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