创建自定义对象时，如何停止从两个类似的命名为XML节点获取对象？

Question

我正试图解析几个RSS新闻提要，我将在以后根据我正在寻找的内容进行过滤。每个提要有一个稍微不同的XML，但通常有一个标题、描述、链接和pubDate。有些使用CDATA部分，而有些不使用CDATA部分，因此我为使用CDATA部分的人合并了和if语句。我正在尝试写一个程序来匹配所有的。下面是一个让我头疼的XML示例：

<?xml version="1.0" encoding="UTF-8"?>
<rss xmlns:media="http://search.yahoo.com/mrss/" xmlns:dc="http://purl.org/dc/elements/1.1/" version="2.0">
  <channel>
    <title><![CDATA[ABC7 RSS Feed]]></title>
    <link><![CDATA[https://abc7news.com/feed]]></link>
    <lastBuildDate><![CDATA[Thu, 13 Jan 2022 15:49:04 +0000]]></lastBuildDate>
    <pubDate><![CDATA[Thu, 13 Jan 2022 15:49:04 +0000]]></pubDate>
    <description>Keep up with news from your local ABC station.</description>
    <copyright>Copyright 2022 ABC Inc., KGO-TV San Francisco</copyright>
    <managingEditor>KGO-TVWebTeam@email.disney.com(KGO-TV San Francisco)</managingEditor>
    <webMaster>KGO-TVWebTeam@email.disney.com(KGO-TV San Francisco)</webMaster>
    <language><![CDATA[en]]></language>
    <item>
      <title><![CDATA[Biden gives COVID response update; administration to deploy military teams to hospitals | LIVE]]></title>
      <description><![CDATA[Starting next week, 1,000 military medical personnel will begin arriving to help mitigate staffing crunches at hospitals across the country. ]]></description>
      <pubDate><![CDATA[Thu, 13 Jan 2022 15:38:02 +0000]]></pubDate>
      <link><![CDATA[https://abc7news.com/us-covid-biden-speech-today-hospitalizations/11462828/]]></link>
      <type><![CDATA[post]]></type>
      <guid><![CDATA[https://abc7news.com/us-covid-biden-speech-today-hospitalizations/11462828/]]></guid>
      <dc:creator><![CDATA[AP]]></dc:creator>
      <media:keywords><![CDATA[us covid, biden covid, biden speech today, covid hospitalizations, omicron variant, us hospitals, covid cases, covid omicron, biden military medical teams]]></media:keywords>
      <category><![CDATA[Health & Fitness,omicron variant,Coronavirus,military,joe biden,hospitals,u.s. & world]]></category>
      <guid isPermaLink="false">health/live-biden-highlighting-federal-surge-to-help-weather-omicron/11462828/</guid>
    </item>
    <item>
      <title><![CDATA[Massive backup on Bay Bridge after early morning crash]]></title>
      <description><![CDATA[A massive backup continues on the Bay Bridge after an earlier multi-vehicle crash past Treasure Island.]]></description>
      <pubDate><![CDATA[Thu, 13 Jan 2022 15:30:15 +0000]]></pubDate>
      <link><![CDATA[https://abc7news.com/bay-bridge-crash-traffic-accident-sf-commute/11463119/]]></link>
      <type><![CDATA[post]]></type>
      <guid><![CDATA[https://abc7news.com/bay-bridge-crash-traffic-accident-sf-commute/11463119/]]></guid>
      <dc:creator><![CDATA[KGO]]></dc:creator>
      <media:title><![CDATA[Crash triggers massive backup on Bay Bridge]]></media:title>
      <media:description><![CDATA[A crash on the Bay Bridge triggered massive gridlock for the Thursday morning commute.]]></media:description>
      <media:videoId>11463404</media:videoId>
      <media:thumbnail url="https://cdn.abcotvs.com/dip/images/11463261_011322-kgo-sky7-bay-bridge-traffic-img.jpg" width="1280" height="720" />
      <enclosure url="https://vcl.abcotv.net/video/kgo/011322-kgo-6am-bay-bridge-crash-vid.mp4" length="79" type="video/mp4" />
      <media:keywords><![CDATA[Bay Bridge crash, traffic, accident, SF commute, Oakland drive times, bay bridge toll plaza backup, Bay Area, treasure island,]]></media:keywords>
      <category><![CDATA[Traffic,Treasure Island,Oakland,San Francisco,CHP,bay bridge,crash]]></category>
      <guid isPermaLink="false">traffic/massive-backup-on-bay-bridge-after-early-morning-crash/11463119/</guid>
    </item>
  </channel>
</rss>

下面是将每个项放入对象($posts)中的解析代码：

    $rss = [xml] (Get-Content 'I:\RSS_Project\Feeds\feed-3.xml')
    $rss.SelectNodes('//item')|%{
    $posts += New-Object psobject -Property @{
        Title = If($_.Title."#cdata-section"){$_.Title."#cdata-section"}else{$_.Title}
        Desc = If($_.description."#cdata-section"){$_.description."#cdata-section"}else{$_.Title}
        link = If($_.link."#cdata-section"){$_.link."#cdata-section"}else{$_.link}
        pubDate = If($_.pubDate."#cdata-section"){$_.pubDate."#cdata-section"}else{$_.pubDate}
        
        }
    }

我通过这个提要获得了正确的链接和pubDate，但是因为在某些项目中有一个media:title和media:description (是的，在同一个提要中不一致)，所以我将{title，media:title}输出到我创建的$posts.title自定义对象中。

有了这些数据，它将是{在凌晨崩溃后的海湾桥上的大规模备份，崩溃将触发海湾桥上的大规模备份}。我想不出如何避免捕捉媒体:标题数据。我的其他XML提要没有媒体:title。

如果它存在于任何提要中，我是否可以先发制人并提前删除它？我尝试使用$_.Title，它在这个提要上工作，但是由于其他提要没有数组，所以它不能在这些提要上工作。我有同样的问题，媒体:描述存在于项目中。我将数据输出到一个HTML表中，当我有标题或描述数组时，该表只列出"System.Object“。任何帮助消除媒体:标题进入我的对象将不胜感激。

Answer 1

PowerShell的XML类型适配器可能有点“摇摇欲坠”(因为缺少一个更好的技术术语)，因为它试图简化一些复杂的东西--因此，它只是忽略名称空间前缀并以其本地名称解析节点，从而导致$_.title同时解析<title>和<media:title>元素。

相反，也可以使用XPath解析这些值：

$fields = 'title','description','pubDate','link'

$posts = foreach($item in $rss.SelectNodes('//item')) {
    # create dictionary to hold properties of the object we want to construct
    $properties = [ordered]@{}

    # now let's try to resolve them all
    foreach($fieldName in $fields) {
        # use a relative XPath expression to extract relevant child node from current item
        $value = $item.SelectSingleNode("./${fieldName}")

        # handle content wrapped in CData
        if($value.HasChildNodes -and $value.ChildNodes[0] -is [System.Xml.XmlCDataSection]){
            $value = $value.ChildNodes[0]
        }

        # add node value to dictionary
        $properties[$fieldName] = $value.InnerText
    }

    # output resulting object
    [pscustomobject]$properties
}