Basic xslt transformation - xslt

Question

I have one XML request which I need to modify (to XML) and then send it further. I have no prior knowledge of XSLT.
Say I have
<Combined>
<Profile>
<Fullname>John Doe</Fullname>
<OtherData>
<Birthdate>1996</Birthdate>
<FavoriteBooks>
<Book>
<id>1</id>
<description>Libre1</description>
</Book>
<Book>
<id>2</id>
<description>Libre2</description>
</Book>
<Book>
<id>3</id>
<description></description>
</Book>
<Book>
<id>4</id>
<description>Libre4</description>
</Book>
</FavoriteBooks>
</OtherData>
</Profile>
<LoadedData>
<NewBirthdate>1998</NewBirthdate>
<BooksUpdate>
<Book id="1">
<BookText>Book1</BookText>
</Book>
<Book id="2">
<BookText>Book2</BookText>
</Book>
<Book id="3">
<BookText>Book3</BookText>
</Book>
<Book id="4">
<BookText>Book4</BookText>
</Book>
<Book id="5">
<BookText>Book5</BookText>
</Book>
</BooksUpdate>
</LoadedData>
And want to get
<Profile>
<Fullname>John Doe</Fullname>
<OtherData>
<Birthdate>1998</Birthdate>
<FavoriteBooks>
<Book>
<id>1</id>
<description>Libre1Book1</description>
</Book>
<Book>
<id>2</id>
<description>Libre2Book2</description>
</Book>
<Book>
<id>3</id>
<description>empty</description>
</Book>
<Book>
<id>4</id>
<description>Libre4Book4</description>
</Book>
<Book>
<id>5</id>
<description>new Book5</description>
</Book>
</FavoriteBooks>
</OtherData>
I did a pretty pathetic attempt, which obviously does not work.
<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:msxsl="urn:schemas-microsoft-com:xslt" exclude-result-prefixes="msxsl"
>
<xsl:output method="xml" indent="yes"/>
<xsl:template match="/">
<Profile>
<xsl:apply-templates select="Combined/Profile/Fullname" />
</Profile>
<Otherdata>
<Birthdate>
<xsl:apply-templates select="Combined/LoadedData/NewBirthdate"/>
</Birthdate>
<FavoriteBooks>
<xsl:for-each select="/Combined/Profile/OtherData/FavoriteBooks/Book">
<Book>
<id>
<xsl:value-of select="id"/>
</id>
<description>
<xsl:value-of select="description"/>
<xsl:apply-templates select="/Combined/LoadedData/BooksUpdate/Book[#id='']" />
</description>
</Book>
</xsl:for-each>
</FavoriteBooks>
</Otherdata>
</xsl:template>
</xsl:stylesheet>
How can I get closer to what I want to get? Could you also advise me some book to jump start, because w3schools tutorials are useless :(

Answer 1

How's this?
According to the logic you described, the description would not be "empty" but rather "Book3" (empty string merged with "Book3").
<!-- root and static content -->
<xsl:template match="/">
<xsl:apply-templates select='Combined/Profile' />
</xsl:template>
<!-- identity/copy, with some tweaks -->
<xsl:template match='node()|#*'>
<!-- copy node -->
<xsl:copy>
<!-- add in its attributes -->
<xsl:apply-templates select='#*' />
<!-- now either apply same treatment to child nodes, or something special -->
<xsl:choose>
<!-- use updated birthdate -->
<xsl:when test='name() = "Birthdate"'>
<xsl:value-of select='/Combined/LoadedData/NewBirthdate' />
</xsl:when>
<!-- merge book descriptions -->
<xsl:when test='name() = "description"'>
<xsl:value-of select='concat(., /Combined/LoadedData/BooksUpdate/Book[#id = current()/../id]/BookText)' />
</xsl:when>
<!-- or just keep recursing -->
<xsl:otherwise>
<xsl:apply-templates select='node()' />
</xsl:otherwise>
</xsl:choose>
</xsl:copy>
<!-- if we've done all books, add in any in the loaded data but not the original data -->
<xsl:if test='name() = "Book" and not(count(following-sibling::Book))'>
<xsl:variable name='orig_book_ids'>
<xsl:for-each select='../Book'>
<xsl:value-of select='concat("-",id,"-")' />
</xsl:for-each>
</xsl:variable>
<xsl:apply-templates select='/Combined/LoadedData/BooksUpdate/Book[not(contains($orig_book_ids, concat("-",#id,"-")))]' mode='new_books' />
</xsl:if>
</xsl:template>
<!-- new books -->
<xsl:template match='Book' mode='new_books'>
<Book>
<id><xsl:value-of select='#id' /></id>
<description>new <xsl:value-of select='BookText' /></description>
</Book>
</xsl:template>
You can run it at this XMLPlayground session (see output source).