Almost empty transformed XML

Question

I am new to XSLT and I am asking for some help. I need to transform simple XML file to another XML. Here's the first one:

<?xml version="1.0" encoding="utf-8"?>
<library xmlns="http://example.net/library/1.0">
    <authors>
        <author id="a1">
            <name>John</name>
            <surname>Applesed</surname>
            <born>1979-11-11</born>
        </author>
        <author id="a2">
            <name>Krzysztof</name>
            <surname>Habdank</surname>
            <born>1965-12-12</born>
        </author>
        <author id="a3">
            <name>Paulo</name>
            <surname>Coelho</surname>
            <born>1915-06-17</born>
        </author>
        <author id="a4">
            <name>Mikołaj</name>
            <surname>Kopernik</surname>
            <born>1473-02-19</born>
            <died>1543-05-24</died>
        </author>
    </authors>
    <books>
        <book id="b1" author-id="a1">
            <title>Missing opportunity</title>
            <published>1992</published>
            <isbn>978-3-16-148410-0</isbn>
        </book>
        <book id="b2" author-id="a4">
            <title>O obrotach sfer niebieskich</title>
            <published>1543</published>
        </book>
    </books>
</library>

Here's the format I want to get:

<?xml version="1.0" encoding="utf-8"?>
<books xmlns="http://example.net/books/1.0" xmlns:a="http://example.net/author/1.0">
    <book>
        <a:author>
            <a:name>John</a:name>
            <a:surname>Applesed</a:surname>
        </a:author>
        <title>Missing opportunity</title>
    </book>
    <book>
        <a:author>
            <a:name>Mikołaj</a:name>
            <a:surname>Kopernik</a:surname>
        </a:author>
        <title>O obrotach sfer niebieskich</title>
    </book>
</books>

And here's what i managed to code:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
<xsl:output method="xml" indent="yes"/>

<xsl:template match="/">
  <books xmlns="http://example.net/books/1.0" xmlns:a="http://example.net/author/1.0">
     <xsl:for-each select="library/authors/author[@id='id']">
       <book>
         <name><xsl:value-of select="@name"/></name>
         <surname><xsl:value-of select="@surname"/></surname>
       </book>
     </xsl:for-each>
  </books>
</xsl:template>

</xsl:stylesheet>

Unfortunately, all I got is:

<?xml version="1.0" encoding="UTF-8"?>
<books xmlns="http://example.net/books/1.0" xmlns:a="http://example.net/author/1.0" />

My source of knowledge: https://msdn.microsoft.com/en-us/library/ms766462(v=vs.85).aspx

I was checking effect on this site:

http://www.freeformatter.com/xsl-transformer.html#ad-output

Thanks for your time and effort.

Answer 1

The stylesheet that produces the desired output looks like this:

<xsl:stylesheet
    version="1.0"
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:l="http://example.net/library/1.0"
    xmlns:a="http://example.net/author/1.0"
    xmlns="http://example.net/books/1.0"
    exclude-result-prefixes="l"
>
    <xsl:output method="xml" indent="yes"/>

    <xsl:template match="/l:library">
        <xsl:apply-templates select="l:books" />
    </xsl:template>

    <xsl:template match="l:books">
        <books>
            <xsl:apply-templates select="l:book" />
        </books>
    </xsl:template>

    <xsl:template match="l:book">
        <xsl:variable name="author" select="//l:author[@id = current()/@author-id]" />
        <book>
            <a:author>
                <a:name><xsl:value-of select="$author/l:name" /></a:name>
                <a:surname><xsl:value-of select="$author/l:surname" /></a:surname>
            </a:author>
            <title><xsl:value-of select="l:title" /></title>
        </book>
    </xsl:template>
</xsl:stylesheet>

Notes:

• Every XML namespace you intend to use (input or output) should be declared at the <xsl:stylesheet>.
• One of them can become the default namespace (here it's http://example.net/books/1.0), which can be recognized by the fact that no prefix is registered. Every unprefixed element in the stylesheet will be in this namespace.
• All other XML namespaces need a prefix, here I chose l for the library namespace and a for the author namespace, but you can use any prefix you like.
• All namespaces that should not appear in the output document can be suppressed via exclude-result-prefixes
• You can store nodes in variables as shown with the $authors variable.
• The current() function lets you refer inside XPath expressions to the node that the XSLT processor is currently working on.
• Nodes that are in a default namespace in the input document must be referred to using a prefix, like in this case with l.
• Try to prefer <xsl:template>/<xsl:apply-templates> when writing stylesheets.