How do I add XML namespace as attribute prefix in PowerShell?

Question

I want to generate the following XML using Powershell v3

<?xml version="1.0" encoding="UTF-8"?>
<AMXML xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="http://registration.somewhere.com/schemas/something.xsd">
  <Type>Something</Type>
</AMXML>

and I've got the following code so far

[xml]$doc = New-Object System.Xml.XmlDocument
$dec = $doc.CreateXmlDeclaration("1.0", "UTF-8", $null)
$doc.AppendChild($dec) | Out-Null

$root = $doc.CreateNode("element","AMXML",$null)

$att = $doc.CreateAttribute("xmlns:xsi")
$att.Value = "http://www.w3.org/2001/XMLSchema-instance"
$root.Attributes.Append($att) | Out-Null

$att1 = $doc.CreateAttribute("xsi:noNamespaceSchemaLocation")
$att1.Value = "http://registration.somewhere.com/schemas/something.xsd"
$root.Attributes.Append($att1) | Out-Null

$x = $doc.CreateNode("element", "Type", $null)
$x.InnerText = "Something"
$root.AppendChild($x) | Out-Null

$doc.AppendChild($root) | Out-Null

$doc.InnerXml

Which produces

<?xml version="1.0" encoding="UTF-8"?>
<AMXML xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" noNamespaceSchemaLocation="http://registration.somewhere.com/schemas/something.xsd">
  <Type>Something</Type>
</AMXML>

Despite creating the attribute xsi:noNamespaceSchemaLocation the output removes the xsi: prefix, leaving just noNamespaceSchemaLocation="http://registration.some where.com/schemas/something.xsd" which fails my xsd.

I've tried various overloads of CreateAttribute() which results in extra attributes or swapped prefixes.

Where am I going wrong?

Answer 1

You need to create the attribute in the xsi namespace:

$xsi_uri = 'http://www.w3.org/2001/XMLSchema-instance'

$att1 = $doc.CreateAttribute('xsi', 'noNamespaceSchemaLocation', $xsi_uri)
$att1.Value = "http://registration.somewhere.com/schemas/something.xsd"
$root.Attributes.Append($att1) | Out-Null