带有谓词和条件的XPath表达式

Question

我的XPath表达式中的错误在哪里？我需要检索所有上传的视频的平均等级大于或等于3的所有用户的配置文件

<?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

有XPath中没有avg()功能1.0（我怀疑你在这里使用）。

试试这个：

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

或者略短的变体：

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

---

从那里往<user>对象的列表很简单：

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

---

或者，当avg()可作为一个功能，因为你使用XPath 2.0及以上版本中，甚至更短：的XPath

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