XPath 谓词

17 Mar 2025 | 阅读 2 分钟

断言使用方括号编写 XPath 表达式。它用于根据某些条件限制节点集中选定的节点。请参阅“employee”示例中断言的用法。

Employee.xml

<?xml version = "1.0"?>
<?xml-stylesheet type = "text/xsl" href = "employee.xsl"?>
<class>
   <employee id = "001">
      <firstname>Abhiram</firstname>
      <lastname>Kushwaha</lastname>
      <nickname>Manoj</nickname>
      <salary>15000</salary>
   </employee>
   <employee id = "002">
      <firstname>Akash</firstname>
      <lastname>Singh</lastname>
      <nickname>Bunty</nickname>
      <salary>25000</salary>
   </employee>
    <employee id = "003">
      <firstname>Brijesh</firstname>
      <lastname>Kaushik</lastname>
      <nickname>Ballu</nickname>
      <salary>20000</salary>
   </employee>
    <employee id = "004">
      <firstname>Zoya</firstname>
      <lastname>Mansoori</lastname>
      <nickname>Sonam</nickname>
      <salary>30000</salary>
   </employee>
</class>

索引	谓词	描述
1)	/class/employee[1]	它将选择作为 class 元素的子元素的第一个 employee 元素。
2)	/class/employee[last()]	它将选择作为 class 元素的子元素的最后一个 employee 元素。
3)	/class/employee[@id = 002]	它将选择 id 为 002 的 employee 元素。
4)	/class/salary[salary > 10000]	它将选择工资大于 10000 的 employee 元素。

XPath 断言示例

让我们举一个例子，通过迭代每个 employee，创建一个包含 <employee> 元素及其详细信息的表。此示例使用断言来计算 employee 节点的位置，然后打印 employee 详细信息。

Employee.xml

<?xml version = "1.0"?>
<?xml-stylesheet type = "text/xsl" href = "employee.xsl"?>
<class>
   <employee id = "001">
      <firstname>Abhiram</firstname>
      <lastname>Kushwaha</lastname>
      <nickname>Manoj</nickname>
      <salary>15000</salary>
   </employee>
   <employee id = "002">
      <firstname>Akash</firstname>
      <lastname>Singh</lastname>
      <nickname>Bunty</nickname>
      <salary>25000</salary>
   </employee>
    <employee id = "003">
      <firstname>Brijesh</firstname>
      <lastname>Kaushik</lastname>
      <nickname>Ballu</nickname>
      <salary>20000</salary>
   </employee>
    <employee id = "004">
      <firstname>Zoya</firstname>
      <lastname>Mansoori</lastname>
      <nickname>Sonam</nickname>
      <salary>30000</salary>
   </employee>
</class>

Employee.xsl

<?xml version = "1.0" encoding = "UTF-8"?>
<xsl:stylesheet version = "1.0"
   xmlns:xsl = "http://www.w3.org/1999/XSL/Transform">  
   <xsl:template match = "/">
      <html>
         <body>
            <h2>Employee</h2>
            <table border = "1">
               <tr bgcolor = "pink">	 
                  <th>ID</th>
                  <th>First Name</th>
                  <th>Last Name</th>
                  <th>Nick Name</th>
                  <th>Salary</th>	  
               </tr>					
               <xsl:for-each select = "/class/employee[1]">
                  <tr>	 
                     <td><xsl:value-of select = "@id"/></td>
                     <td><xsl:value-of select = "firstname"/></td>
                     <td><xsl:value-of select = "lastname"/></td>
                     <td><xsl:value-of select = "nickname"/></td>
                     <td><xsl:value-of select = "salary"/></td>	 
                  </tr>	
               </xsl:for-each>					
               <xsl:for-each select = "/class/employee[last()]">
                  <tr>	 
                     <td><xsl:value-of select = "@id"/></td>
                     <td><xsl:value-of select = "firstname"/></td>
                     <td><xsl:value-of select = "lastname"/></td>
                     <td><xsl:value-of select = "nickname"/></td>
                     <td><xsl:value-of select = "salary"/></td>	 
                  </tr>	
               </xsl:for-each>	
               <xsl:for-each select = "/class/employee[@id = 002]">
                  <tr>	 
                     <td><xsl:value-of select = "@id"/></td>
                     <td><xsl:value-of select = "firstname"/></td>
                     <td><xsl:value-of select = "lastname"/></td>
                     <td><xsl:value-of select = "nickname"/></td>
                     <td><xsl:value-of select = "salary"/></td>	 
                  </tr>	
               </xsl:for-each>
               <xsl:for-each select = "/class/employee[salary > 10000]">
                  <tr>	 
                     <td><xsl:value-of select = "@id"/></td>
                     <td><xsl:value-of select = "firstname"/></td>
                     <td><xsl:value-of select = "lastname"/></td>
                     <td><xsl:value-of select = "nickname"/></td>
                     <td><xsl:value-of select = "salary"/></td>	 
                  </tr>	
               </xsl:for-each>		
            </table> 
         </body>
      </html>
   </xsl:template>
</xsl:stylesheet>

输出

注意: 在上面的示例中，你可以看到所有四个查询都被获取了。

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