How to use of XPath Predicates in XML

In this article I will explain the predicates in XPath.
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Introduction

Predicates are used to find a specific node/element or a node that contains a specific value.Predicates are always embedded in square brackets,like inside [ ].The following are some  path expressions with predicates and the result of the expressions based on the below example,

Example

<?xml version="1.0" encoding="utf-8" ?>

<Employee>

  <Trainee>

    <Name>Harry</Name>

    <id>1234</id>

    <Salary>10k</Salary>

    <address street="12">Delhi</address>

  </Trainee>

  <Trainee>

    <Name>Georage</Name>

    <id>1432</id>

    <Salary>20k</Salary>

    <address street="10">Delhi</address>

  </Trainee>

</Employee>

 

Now the following lines shows that how the nodes of above example represents the path expressions of predicates.

  • /Employee/Trainee[1]  :  Selects the first Trainee element that is the child of the Employee element.

  • /Employee/Trainee[last()]  :  Selects the last Trainee element that is the child of the Employee element.

  • /Employee/Trainee[last()-1]  :   Selects the last but one Trainee element that is the child of the Employee element.

  • /Employee/Trainee[position()<3]  :  Selects the first two Trainee elements that are children of the Employee element.

  • //address[@street]  :  Selects all the address elements that have an attribute named street.

  • //address[@street="12"]  :  Selects all the address elements that have an attribute named street with a value of "12".

  • /Employee/Trainee[salary>15k]  :  Selects all the Trainee elements of the Employee element that have a salary element with a value greater than 15k.

  • /Employee/Trainee[salary>15k]/address  :  Selects all the address elements of the Trainee elements of the Employee element that have a salary element with a value greater than 15k.

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