xml - 带有谓词和条件的XPath表达式

Question

XPath表达中的错误在哪里？我需要检索所有上传的视频的平均评分均大于或等于3的所有用户的个人资料。

    <?xml version="1.0" encoding="UTF-8"?>
<smileyvideo>
   <video id="8628149">
      <uploader>satsuya.oda@example.com</uploader>
      <title>Bad Apple</title>
      <ratings>
         <rating user="epwager@example.com" value="1" />
         <rating user="ajenk@example.com" value="2" />
      </ratings>
   </video>
   <video id="123456">
      <uploader>ajenk@example.com</uploader>
      <title>Musician Cat</title>
      <ratings>
         <rating user="satsuya.oda@example.com" value="3" />
         <rating user="epwager@example.com" value="3" />
         <rating user="ajenk@example.com" value="4" />
      </ratings>
   </video>
   <video id="474920">
      <uploader>satsuya.oda@example.com</uploader>
      <title>Shrek</title>
      <ratings>
         <rating user="epwager@example.com" value="1" />
         <rating user="ajenk@example.com" value="1" />
      </ratings>
   </video>
   <!-- Users List -->
   <user>
      <name>Emil P. Wager</name>
      <email>epwager@example.com</email>
   </user>
   <user>
      <name>Satsuya Oda</name>
      <email>satsuya.oda@example.com</email>
   </user>
   <user>
      <name>Anthony J. Jenkins</name>
      <email>ajenk@example.com</email>
      <bio>I am a food scientist, currently working in iceland. Make sure to
check out my blog!</bio>
   </user>
</smileyvideo>

我的XPath表达式是

//user[preceding-sibling::video/uploader[avg((following-sibling::ratings/rating/@value))>=3]/text()=//user/email/text()]

Answer 1

XPath 1.0中没有avg()函数（我怀疑您在这里使用）。

试试这个：

//video[sum(ratings/rating/@value) div count(ratings/rating) >= 3]/uploader

或者，稍微短一些的变体：

//video[ratings[sum(rating/@value) div count(rating) >= 3]]/uploader

从那里转到 <user>对象列表很简单：

//user[email = //video[ratings[sum(rating/@value) div count(rating) >= 3]]/uploader]

或者，当由于使用XPath 2.0+而使 avg()作为功能可用时，甚至更短：

//user[email = //video[avg(ratings/rating/@value) >= 3]/uploader]