XSLT Parameters

 

The <xsl:param> element in XSLT (Extensible Stylesheet Language Transformations) is used to define parameters that can be passed into templates. Parameters allow you to pass values into templates, making your XSLT transformations more flexible and reusable. Here's how <xsl:param> works in detail:

Basic Syntax:

<xsl:param name="parameterName" select="expression"/>

name Attribute: Specifies the name of the parameter. This is how you refer to the parameter within the template.

select Attribute (Optional): Specifies an XPath expression whose result will be the initial value of the parameter. If not provided, the parameter is initially empty.

Usage:

Defining Parameters:

Parameters are typically defined at the beginning of a template or an XSLT stylesheet.

<xsl:param name="paramName" select="'default value'"/>

In this example, a parameter named paramName is defined with an initial value of 'default value'.

Passing Parameters:

Parameters can be passed into templates using <xsl:with-param> within <xsl:call-template> or <xsl:apply-templates>.

<xsl:call-template name="TemplateName">

    <xsl:with-param name="paramName" select="someValue"/>

</xsl:call-template>

In this example, the paramName parameter is passed with the value of someValue to the template named TemplateName.

Accessing Parameters:

Inside the template, parameters are accessed using the $ symbol followed by the parameter name.

<xsl:template name="TemplateName">

    <xsl:param name="paramName"/>

    <!-- Use $paramName in the template -->

</xsl:template>

In this template, the value of the paramName parameter can be used within the template logic.

Use Cases:

Reusability:

Parameters allow you to reuse templates with different values. For instance, a generic template can be customized by passing different parameters.

Dynamic Logic:

Parameters enable the dynamic adjustment of template logic based on values passed into the template. Different transformations can be applied to the same template based on parameter values.

Configuration:

Parameters can be used for configuration settings, allowing you to adjust the behavior of your transformations without modifying the XSLT code.

<xsl:param name="dateFormat" select="'MM/dd/yyyy'"/>

In this example, the dateFormat parameter can be used throughout the XSLT stylesheet to format dates, and its value can be easily changed without modifying the rest of the code.

Note:

Parameters are local to the template where they are defined. They do not retain values between different template calls or apply-templates calls.

Parameters provide a way to make your XSLT transformations more dynamic and adaptable, allowing you to create versatile stylesheets capable of handling various scenarios.

Parameters

Applying Parameters

Parameters enable you to customize the transformation of XML documents. 

You can use parameters to selectively retrieve data from an XML document.

The <xsl:param> and <xsl:with-param> elements enable you to create and use parameters in an XSLT document.

There are two types of parameters, global and local. 

 If a parameter is declared or created within the <xsl:stylesheet> or <xsl:transform> elements, the scope of the parameter is global.

If the parameter created is within the template body, it is local to that particular template.

The syntax for the <xsl:param> element is:

<xsl:param name=Qname select=Expression as = sequence-type required="yes"> <!-- Content: sequence-constructor </xsl:param>

• name: Defines the name of the parameter. The name of the parameter needs to be a qualified name, and can have optional namespace prefixes. If the prefix exists, you need to provide the namespace URI.

• select: Specifies a value for the parameter, which is the default value. You can also assign an expression to this attribute. The result of the expression is the value of the parameter. Most of the expressions return Boolean, number, string, or node-set datatypes.

• required: Specifies whether the parameter is compulsory or optional. You cannot use this attribute for function parameters. The default value is no.

• as: Specifies the datatype of the parameter. The value assigned to the parameter is converted to this type using the argument conversion rules.

• creates a parameter, empname, of the string datatype, and assigns a value, John, to it:<xsl:param name="empname" as="xs:string" > John</xsl:param>

Assigning Parameter Values

You can use the <xsl:with-param> element to assign values to parameters that are declared using the <xsl:param name> element. You can use the <xsl:with-param> element within the <xsl:template>, <xsl:call-template>, <xsl:apply-templates>, <xsl:apply-imports> elements, as required by the document.

The syntax of the <xsl:with-param> element is:

<xsl:with-param name =Qname select=Expression> template body </xsl:with-param>

In the above syntax, the name attribute specifies the parameter name, and the select attribute assigns a value to the parameter.

The name and select attributes of this element are similar to that of the <xsl:param> element. 

 For example, you can use the <xsl:param> and the <xsl:with-param> elements to retrieve and display information in an XML document.