🔀 XSLT <xsl:choose> – Advanced Conditional Logic with Multiple Branches

🧲 Introduction – Why Learn <xsl:choose>?

While <xsl:if> handles basic conditions, what if you need multiple branches, like a classic if…else if…else structure? That’s exactly what <xsl:choose> offers. It allows you to define multiple conditions and fallback logic using <xsl:when> and <xsl:otherwise>, giving you full control over how your transformation responds to different XML content.

🎯 In this guide, you’ll learn:

• What <xsl:choose> is and how it works
• How to use <xsl:when> and <xsl:otherwise>
• Examples of complex conditional rendering in XML
• Best practices and common mistakes to avoid

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🧾 Syntax of <xsl:choose>

<xsl:choose>
  <xsl:when test="XPathExpression1">
    <!-- output if first condition is true -->
  </xsl:when>
  <xsl:when test="XPathExpression2">
    <!-- output if second condition is true -->
  </xsl:when>
  <xsl:otherwise>
    <!-- fallback if no conditions are true -->
  </xsl:otherwise>
</xsl:choose>

• Use one or more <xsl:when> for conditional branches
• Use <xsl:otherwise> for fallback content (optional but recommended)

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📄 Sample XML

<book>
  <title>Mastering XSLT</title>
  <price>499</price>
</book>

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✅ Example – Price-Based Labels

<xsl:choose>
  <xsl:when test="price &lt; 300">
    <p><strong>Budget</strong></p>
  </xsl:when>
  <xsl:when test="price &lt; 600">
    <p><strong>Standard</strong></p>
  </xsl:when>
  <xsl:otherwise>
    <p><strong>Premium</strong></p>
  </xsl:otherwise>
</xsl:choose>

✅ Output for <price>499</price>:

<p><strong>Standard</strong></p>

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🧠 Example – Check Attribute with Fallback

<xsl:choose>
  <xsl:when test="@status='in-stock'">
    <p>Available Now</p>
  </xsl:when>
  <xsl:when test="@status='preorder'">
    <p>Pre-Order Available</p>
  </xsl:when>
  <xsl:otherwise>
    <p>Out of Stock</p>
  </xsl:otherwise>
</xsl:choose>

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🔁 Use Inside <xsl:for-each>

<xsl:for-each select="catalog/book">
  <h3><xsl:value-of select="title"/></h3>
  <xsl:choose>
    <xsl:when test="price &lt; 400">
      <p>Discounted</p>
    </xsl:when>
    <xsl:otherwise>
      <p>Regular Price</p>
    </xsl:otherwise>
  </xsl:choose>
</xsl:for-each>

✅ Dynamically labels each book based on its price.

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🧾 Multiple Conditions in One Test

<xsl:when test="@type='ebook' and price &lt; 200">
  <p>Affordable eBook</p>
</xsl:when>

✅ You can use logical operators: and, or, not() in the test condition.

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⚠️ <xsl:choose> vs <xsl:if>

Feature	<xsl:choose>	<xsl:if>
Multi-branch	✅ Supports multiple when conditions	❌ Single condition only
Else logic	✅ via <xsl:otherwise>	❌ No else branch
Use case	Complex branching, mutually exclusive	Simple true/false tests

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✅ Best Practices for <xsl:choose>

• ✔️ Use when multiple outcomes are possible
• ✔️ Always include <xsl:otherwise> to handle unexpected values
• ✔️ Use clear, non-overlapping conditions in test attributes
• ❌ Don’t mix with <xsl:if> for the same logic—it reduces readability

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📌 Summary – Recap & Next Steps

<xsl:choose> gives you full control over conditional rendering in XML transformations. With it, you can handle branching logic, default values, and multiple rules—just like if/else structures in other programming languages.

🔍 Key Takeaways:

• Use <xsl:choose> for multi-branch decision making
• Pair with <xsl:when> for conditions and <xsl:otherwise> for defaults
• Works great inside loops and templates for dynamic rendering

⚙️ Real-world relevance: Used in templating engines, decision trees, XML-based configuration display, e-commerce pricing labels, and content variations.

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❓ FAQs – XSLT <choose>

❓ Is <xsl:otherwise> required?
✅ No, but it’s recommended to catch all unmatched cases.

❓ Can I nest <xsl:choose> inside another?
✅ Yes. Nested conditionals are valid.

❓ Can I combine conditions in test?
✅ Yes. Use XPath operators like and, or, and not().

❓ Can <xsl:choose> replace all uses of <xsl:if>?
✅ Technically yes, but <xsl:if> is better for single, simple conditions.

❓ What happens if none of the <xsl:when> tests match?
✅ The <xsl:otherwise> block is executed (if present); otherwise, no output.

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