XSL Concepts: Conditions and Loops. Robert Kiffe, Senior Web Developer OmniUpdate, Inc.

Transcription

1 XSL Concepts: Conditions and Loops Robert Kiffe, Senior Web Developer OmniUpdate, Inc.

2 Quick XSL Recap Conditional Statements If Choose XPath Conditional Loops For-Each For-Each-Group Apply-Templates Activities! Agenda

3 XSL Recap Since not everyone uses XSL every day!

4 extensible Stylesheet Language In most cases: XML + XSL = HTML OU Campus utilizes a one-time XSL transformation upon publishing to the production server

5 XSL XSL consists of a subset of smaller language sets: XSLT Instruction elements that start with <xsl: Official Reference: lt-30/ XPath Syntax and functions for navigating and manipulating XML structures Official Reference: 30/ XQuery (SQL-like language we don t need to worry about that right now)

6 To What End? Add flexibility in changing the final output What does XSL allow us to do? Also (but we don t care right now): Multiple Outputs Extra logic to replace ServerSide scripts Content Re-Use Transform simple content into more complex structures

7 Conditional Statements Should I do this? Yes, yes you should.

8 <xsl:if> Format: <xsl:if test="$x = 4"> </xsl:if> Simple check against a single condition Conditional boolean must evaluate to 'true' for sequence constructor (contents) to be enabled No 'else' statement! Helpful Operators: not() and, or gt, ge, lt, le

9 <xsl:choose> Format: <xsl:choose> <!-- $temp is a temperature in Celsius --> <xsl:when test="$temp le 0"> <state>solid</state> </xsl:when> <xsl:when test="$temp lt 100"> <state>liquid</state> </xsl:when> <xsl:otherwise> <state>gas</state> </xsl:otherwise> </xsl:choose>

10 <xsl:choose> Unlimited 'when' instructions are allowed First matching condition 'wins' Only a single 'otherwise' instruction is allowed (equivalent to "else")

11 XPath Conditional Can be used anywhere in an XPath expression Format: "if ([Condition]) then [XPath] else [XPath]" Nesting conditionals inside the 'then' and/or 'else' expression is valid Parentheses around the 'condition' are required!

12 XPath Conditional Example: <xsl:value-of select=" if ($temp le 0) then 'Solid' else if ($temp lt 100) then 'Liquid' else 'Gas' "/>

13 Loops Gotta iterate 'em all!

14 For-Each Format: <xsl:for-each select="items/item"> </xsl:for-each> Iterate through every matching 'item' in the 'select' expression To sort, nest the following directly after the opening 'for-each' tag: <xsl:sort select= [XPath]" order= [ascending descending]"/>

15 For-Each XPath's active context is the current iteration's matched item Tip: use XPath's position() function to get the current iteration count (note: starts at 1, not 0) Final output is a concatenation of the sequence constructors (aka a 'concatenated sequence of items')

16 For-Each Example (XML) <courses> <course> <id>134</id> <title>intro to Psychology</title> </course> <course> <id>156</id> <title>calculus I</title> </course> [ ] </courses>

17 For-Each Example (XSL) Iterate through all courses: <h3>list of Courses</h3> <ul class="course-list"> <xsl:for-each select="courses/course"> <xsl:sort select="./id" /> <li> <xsl:value-of select="concat(id, ' - ', title)" /> <!-- Output: "134 - Intro to Psychology" --> </li> </xsl:for-each> </ul>

18 For-Each-Group Format: <xsl:for-each-group select="items/item" group-by="type > </xsl:for-each> The XSL runs through every matching 'item' in the 'select' expression and puts them into groups of matching 'type' values designated by the "group-by" attribute The actual iteration of this instruction is through each grouping

19 For-Each-Group Sorting is allowed, but will only sort the groups, not individual items XPath's active context is the current iteration's group of items (as a collection) All grouping methods allowed (but only one at a time): group-by (XPath expression) group-adjacent (XPath expression) group-starting-with (Pattern) group-ending-with (Pattern)

20 For-Each-Group Example (XML) <courses> <course> <subject>english</subject> <!-- NEW --> <id>134</id> <title>writing Composition</title> </course> <course> <subject>mathematics</subject> <!-- NEW --> <id>156</id> <title>calculus I</title> </course> [ ] </courses>

21 For-Each-Group Example (XSL) Iterate through all courses, grouped by Subject: <xsl:for-each-group select="courses/course" group-by="subject"> <h3><xsl:value-of select="current-grouping-key()" /></h3> <ul class="course-list"> <xsl:for-each select="current-group()"> <xsl:sort select="id" /> <li> <xsl:value-of select="concat(id, ' - ', title)" /> <!-- Output: "134 - Writing Composition" --> </li> </xsl:for-each> </ul> </xsl:for-each-group>

22 Loops via Apply-Templates Passive transformations for the lazy (read: smart )

23 Template Rules Format: <xsl:template match="course"/> Purpose: to define how an element or piece of content in the source XML should be transformed Can be used instead of a manual iteration (for-each)

24 Best used: Template Rules When the target is embedded in other content Or when the iteration code should be reusable Pro-Tip: Parameters can be used too! Pro-Tip: You can sort targeted elements inside your "apply-templates" element

25 Example (Source XML) <courses> <course> <id>134</id> <title>intro to Psychology</title> </course> <course> <id>156</id> <title>calculus I</title> </course> [ ] </courses>

26 Matching Courses (XSL) Iterate through all courses: <h3>list of Courses</h3> <ul class="course-list"> <xsl:apply-templates select="courses/course" /> </ul> Define the template rule (transformation): <xsl:template match="course"> <li> <xsl:value-of select="concat(id, ' - ', title)" /> <!-- Output: "134 - Intro to Psychology" --> </li> </xsl:template>

27 Template Rule Priority It is possible to have multiple 'template rules' or 'matches' for a target item within any one 'mode' Priority follows these rules: 1. Import precedence (Rule defined on imported XSL?) 2. Highest priority ('priority' attribute set on template) 3. Default Priority Rules: Complex set of rules based on how specific a definition is to the matched target 30/#default-priority Example: match="p" has more priority than match="node()"

28 Using Modes For transforming the same source content into a different output Takes effect before the Template Priority Rules No mode defined? Same as mode="#unnamed"

29 Using Modes Example Rule: <xsl:template match="course" mode="table"/> <tr> <td><xsl:value-of select="id" /></td> <td><xsl:value-of select="title" /></td> <tr> </xsl:template> Example Call: <xsl:apply-templates select="courses/course" mode="table"/>

30 Questions? And now for the fun part!

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