XPath - Predicate

Predicate refers to the XPath expression written in square brackets. It refers to restrict the selected nodes in a node set for some condition. For example,

S.No.	Predicate & Description
1	/class/student[1] Select first student element which is child of the class element.
2	/class/student[last()] Select last student element which is child of the class element.
3	/class/student[@rolllno = 493] Select student element with rollno 493.
4	/class/student[marks>85] Select student element with marks > 85.

Example

This example creates a table of <student> element with their details, by iterating over each student. It calculates the position of the student node and then prints the student(s) details along with serial no.

students.xml

<?xml version = "1.0"?>
<?xml-stylesheet type = "text/xsl" href = "students.xsl"?>
<class>
   <student rollno = "393">
      <firstname>Dinkar</firstname>
      <lastname>Kad</lastname>
      <nickname>Dinkar</nickname>
      <marks>85</marks>
   </student>
   <student rollno = "493">
      <firstname>Vaneet</firstname>
      <lastname>Gupta</lastname>
      <nickname>Vinni</nickname>
      <marks>95</marks>
   </student>
   <student rollno = "593">
      <firstname>Jasvir</firstname>
      <lastname>Singh</lastname>
      <nickname>Jazz</nickname>
      <marks>90</marks>
   </student>
</class>

students.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>Students</h2>
            <table border = "1">
               <tr bgcolor = "#9acd32">	 
                  <th>Roll No</th>
                  <th>First Name</th>
                  <th>Last Name</th>
                  <th>Nick Name</th>
                  <th>Marks</th>	  
               </tr>
					
               <xsl:for-each select = "/class/student[1]">
                  <tr>	 
                     <td><xsl:value-of select = "@rollno"/></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 = "marks"/></td>	 
                  </tr>	
               </xsl:for-each>
					
               <xsl:for-each select = "/class/student[last()]">
                  <tr>	 
                     <td><xsl:value-of select = "@rollno"/></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 = "marks"/></td>	 
                  </tr>	
               </xsl:for-each>
	
               <xsl:for-each select = "/class/student[@rollno = 493]">
                  <tr>	 
                     <td><xsl:value-of select = "@rollno"/></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 = "marks"/></td>	 
                  </tr>	
               </xsl:for-each>

               <xsl:for-each select = "/class/student[marks > 85]">
                  <tr>	 
                     <td><xsl:value-of select = "@rollno"/></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 = "marks"/></td>	 
                  </tr>	
               </xsl:for-each>
	
	
            </table>
  
         </body>
      </html>
   </xsl:template>
</xsl:stylesheet>

Verify the output