flat xml to hierarchical xml using xslt

Question

Trying to create a transformation that will map a flat xml with parent/child ids into a hierarchical structure. I have included a simple request and response examples below. Any help would be really appreciated! Thanks!

Input xml:

<?xml version="1.0" encoding="UTF-8"?>
<Rowset>
    <Row>
        <id>5</id>
        <header>grouptile1</header>
        <parentid>NULL</parentid>
    </Row>
    <Row>
        <id>1</id>
        <header>Grp1 HeaderTile 1-1</header>
        <subheader>Grp1 HeaderTile 1-1</subheader>
        <parentid>5</parentid>
    </Row>
    <Row>
        <id>2</id>
        <header>Grp1 HeaderTile 2-1</header>
        <subheader>Grp1 HeaderTile 2-1</subheader>
        <parentid>5</parentid>
    </Row>
    <Row>
        <id>6</id>
        <header>grouptile2</header>
        <parentid>NULL</parentid>
    </Row>
    <Row>
        <id>3</id>
        <header>Grp1 HeaderTile 2-1</header>
        <subheader>Grp1 HeaderTile 2-1</subheader>
        <parentid>6</parentid>
    </Row>
    <Row>
        <id>4</id>
        <header>Grp1 HeaderTile 2-2</header>
        <subheader>Grp1 HeaderTile 2-2</subheader>
        <parentid>6</parentid>
    </Row>
</Rowset>

Convert to the Output xml:

<?xml version="1.0" encoding="UTF-8"?>
<tiles>
  <grouptile>
    <id>5</id>
    <header>grouptile1</header>
    <tile>
        <id>1</id>
        <header>Grp1 HeaderTile 1-1</header>
        <subheader>Grp1 HeaderTile 1-1</subheader>
    </tile>
    <tile>
        <id>2</id>
        <header>Grp1 HeaderTile 2-1</header>
        <subheader>Grp1 HeaderTile 2-1</subheader>
    </tile>
  </grouptile>
  <grouptile>
    <id>6</id>
    <header>grouptile2</header>
    <tile>
        <id>3</id>
        <header>Grp1 HeaderTile 2-1</header>
        <subheader>Grp1 HeaderTile 2-1</subheader>
    </tile>
    <tile>
        <id>4</id>
        <header>Grp1 HeaderTile 2-2</header>
        <subheader>Grp1 HeaderTile 2-2</subheader>
    </tile>
  </grouptile>
</tiles>

What would be the xslt?

Answer 1

If all you have is parent and child, you could do simply:

XSLT 1.0

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

<xsl:key name="children" match="Row" use="parentid"/>

<xsl:template match="/Rowset">
    <tiles>
        <xsl:for-each select="Row[parentid='NULL']">
            <grouptile>
                <xsl:copy-of select="id | header"/>
                <xsl:for-each select="key('children', id)">
                    <tile>
                        <xsl:copy-of select="id | header | subheader"/>
                    </tile>             
                </xsl:for-each>
            </grouptile>
        </xsl:for-each>
    </tiles>
</xsl:template>

</xsl:stylesheet>