PowerShell处理XML去重 保留空VATRegistrationNumber节点

处理XML格式供应商数据时需满足以下规则：

• 删除所有VATRegistrationNumber（增值税注册号）属性值重复的供应商节点
• 所有VATRegistrationNumber属性值为空的供应商节点必须全部保留，不得删除

现有PowerShell脚本运行存在逻辑错误：会将VATRegistrationNumber为空的节点判定为重复项移除，无法满足空值全保留的要求。

<Suppliers xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="urn:supplier:erp-integration">
  <Supplier SupplierNumber="300008755" CorporateGroupID="1000" Name1="PETER GOW" City="LISMORE" VATRegistrationNumber="60185579027" />
  <Supplier SupplierNumber="300008754" CorporateGroupID="1000" Name1="DANIEL PETRUSHNKO" City="SYDNEY" VATRegistrationNumber="52216736429" />
  <Supplier SupplierNumber="300008753" CorporateGroupID="1000" Name1="PEOPLE2PEOPLE" City="SYDNEY" VATRegistrationNumber="" />
  <Supplier SupplierNumber="300008752" CorporateGroupID="1000" Name1="PEARL CLEANING" City="WOONONA" VATRegistrationNumber="29169648828" />
  <Supplier SupplierNumber="300008751" CorporateGroupID="1000" Name1="PATTO'S PAINTLESS" City="TAMWORTH" VATRegistrationNumber="30482156828" />
  <Supplier SupplierNumber="300008750" CorporateGroupID="1000" Name1="PATRICK ST CLINIC" City="PENGUIN" VATRegistrationNumber="53220182389" />
  <Supplier SupplierNumber="300008749" CorporateGroupID="1000" Name1="MITCHELL PAISH" City="SYDNEY" VATRegistrationNumber="42091590585" />
  <Supplier SupplierNumber="300008748" CorporateGroupID="1000" Name1="PACNET INTERNET" City="MELBOURNE" VATRegistrationNumber="69085213690" />
  <Supplier SupplierNumber="300008747" CorporateGroupID="1000" Name1="NICHOLAS J OWENS" City="SYDNEY" VATRegistrationNumber="32168537004" />
  <Supplier SupplierNumber="300008746" CorporateGroupID="1000" Name1="JOHN O'SULLIVAN" City="SYDNEY" VATRegistrationNumber="51136629180" />
  <Supplier SupplierNumber="300008745" CorporateGroupID="1000" Name1="OSTAR ELECTRICAL" City="BANGALOW" VATRegistrationNumber="47196051022" />
  <Supplier SupplierNumber="300008756" CorporateGroupID="1000" Name1="PKL COURIERS" City="PALM BEACH" VATRegistrationNumber="90690407812" />
  <Supplier SupplierNumber="9008788" CorporateGroupID="2000" Name1="MICHAEL JOHN MCMANUS" City="COBAR" VATRegistrationNumber="51136629180" />
  <Supplier SupplierNumber="9008787" CorporateGroupID="2000" Name1="MOREE PROPERTY" City="MOREE" VATRegistrationNumber="52216736429" />
  <Supplier SupplierNumber="9008786" CorporateGroupID="2000" Name1="PATRICIA GOULD" City="MUDGEE" VATRegistrationNumber="" />
  <Supplier SupplierNumber="9008785" CorporateGroupID="2000" Name1="KAREN DRUCE" City="Warrimoo" VATRegistrationNumber="42091590585" />
  <Supplier SupplierNumber="9008784" CorporateGroupID="2000" Name1="SOLAR SOLUTIONS" City="MUDGEE" VATRegistrationNumber="65164304054" />
  <Supplier SupplierNumber="9008783" CorporateGroupID="2000" Name1="ST GEORGES CHURCH" City="Hurstville" VATRegistrationNumber="79115673239" />
  <Supplier SupplierNumber="9008782" CorporateGroupID="2000" Name1="SHARED VALUE" City="PORT MELBOURNE" VATRegistrationNumber="32168537004" />
  <Supplier SupplierNumber="9008781" CorporateGroupID="2000" Name1="ALLEN KIRK" City="STUARTS POINT" VATRegistrationNumber="" />
  <Supplier SupplierNumber="9008775" CorporateGroupID="2000" Name1="NATIONAL REMOVALS" City="ASHMORE" VATRegistrationNumber="19748626605" />
  <Supplier SupplierNumber="9008774" CorporateGroupID="2000" Name1="INLAND CONTAINER" City="DUBBO" VATRegistrationNumber="78001638777" />
  <Supplier SupplierNumber="9008814" CorporateGroupID="2000" Name1="CTARS PTY LTD" City="SYDNEY" VATRegistrationNumber="59603816593" />
  <Supplier SupplierNumber="9008813" CorporateGroupID="2000" Name1="JENNY &amp; MARSH" City="LAMBTON" VATRegistrationNumber="" />
  <Supplier SupplierNumber="9008812" CorporateGroupID="2000" Name1="ACDMA CENTRE" City="Canley Vale" VATRegistrationNumber="58002378731" />
  <Supplier SupplierNumber="9008999" CorporateGroupID="2000" Name1="CENTRAL HOTEL" City="Sydney" VATRegistrationNumber="47196051022" />
  <Supplier SupplierNumber="9008969" CorporateGroupID="2000" Name1="ALES LICHNER" City="BANGOR" VATRegistrationNumber="" />
</Suppliers>

[xml]$myfile = [xml](Get-content "input.xml")
$nodesToRemove = $myfile.suppliers.childnodes | Group-Object VATRegistrationNumber |
    Foreach-Object { $_.Group | Select-Object -Skip 1 }
    
$nodesToRemove | Foreach-Object {
    $myfile.suppliers.RemoveChild($_)
}
#save XML
$myfile.Save("result.xml")

错误原因是原有分组逻辑未区分空值与非空值，所有节点（包括VAT号为空的节点）都参与了分组去重，空值会被归为同一组，仅保留第一条，其余空值节点被误删。
修正逻辑：仅对非空VAT号的节点执行去重判断，空VAT号节点直接全部保留，不加入待删除列表。

修正后代码：

[xml]$myfile = [xml](Get-Content "input.xml")
# 过滤掉空VAT号的节点，仅对非空VAT做去重校验
$nodesToRemove = $myfile.Suppliers.ChildNodes | 
    Where-Object { -not [string]::IsNullOrEmpty($_.VATRegistrationNumber) } |
    Group-Object VATRegistrationNumber |
    ForEach-Object { $_.Group | Select-Object -Skip 1 }

$nodesToRemove | ForEach-Object {
    $myfile.Suppliers.RemoveChild($_)
}
# 保存处理结果
$myfile.Save("result.xml")

代码修改点说明：

• 新增Where-Object过滤步骤，在分组前就排除VAT号为空的节点，这类节点不会进入重复校验流程，不会被误删
• 非空VAT号的节点沿用原有去重逻辑，同税号仅保留第一条出现的记录，其余重复节点删除，符合去重要求

内容的提问来源于stack exchange，提问作者Jana