I'm currently working on a project that requires me to transform a "flat" XML file into a hierarchical structure.

I'm just getting started with XSLT and wanted to know if I'm heading in the right direction with this approach.

This is my source file (somewhat simplified)

<?xml version="1.0" standalone="yes"?>
<DocumentElement>
  <Orders>
    <OrderID>10248</OrderID>
    <CustomerID>VINET</CustomerID>
    <ProductID>11</ProductID>
    <Quantity>12</Quantity>
    <Discount>0</Discount>
  </Orders>
  <Orders>
    <OrderID>10248</OrderID>
    <CustomerID>VINET</CustomerID>
    <ProductID>42</ProductID>
    <Quantity>10</Quantity>
    <Discount>0</Discount>
  </Orders>
  <Orders>
    <OrderID>10248</OrderID>
    <CustomerID>VINET</CustomerID>
    <ProductID>72</ProductID>
    <Quantity>5</Quantity>
    <Discount>0</Discount>
  </Orders>
  <Orders>
    <OrderID>10250</OrderID>
    <CustomerID>HANAR</CustomerID>
    <ProductID>41</ProductID>
    <Quantity>10</Quantity>
    <Discount>0</Discount>
  </Orders>
  <Orders>
    <OrderID>10250</OrderID>
    <CustomerID>HANAR</CustomerID>
    <ProductID>51</ProductID>
    <Quantity>35</Quantity>
    <Discount>0.15</Discount>
  </Orders>
  <Orders>
    <OrderID>10250</OrderID>
    <CustomerID>HANAR</CustomerID>
    <ProductID>65</ProductID>
    <Quantity>15</Quantity>
    <Discount>0.15</Discount>
  </Orders>
</DocumentElement>


And this is what I want to end up with

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<MyOrders>
  <Order>
    <OrderNumber>10248</OrderNumber>
    <CustomerNumber>VINET</CustomerNumber>
    <OrderLines>
      <ProductID>11</ProductID>
      <ProductID>42</ProductID>
      <ProductID>72</ProductID>
    </OrderLines>
  </Order>
  <Order>
    <OrderNumber>10250</OrderNumber>
    <CustomerNumber>HANAR</CustomerNumber>
    <OrderLines>
      <ProductID>41</ProductID>
      <ProductID>51</ProductID>
      <ProductID>65</ProductID>
    </OrderLines>
  </Order>
</MyOrders>

And here is my attempt to write a stylesheet to produce the result.
It works, but I'm not sure about the for-each part.
Is this the optimal way to go or is it a bad implementation.
I also wonder why I have to put the OrderID into a variable before I can use it as an argument in the for-each select.
Could I access the OrderID directly somehow?


<?xml version="1.0" encoding="UTF-8"?>
<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" standalone="yes"/>
  <xsl:template match="DocumentElement">
    <MyOrders>
      <xsl:apply-templates select="Orders[not(OrderID = preceding::OrderID)]"/>
    </MyOrders>
   </xsl:template>

  <xsl:template match="Orders">
    <xsl:variable name="OrderID" select="OrderID"/>
    <Order>
      <xsl:element name="OrderNumber">
        <xsl:value-of select="OrderID"/>
      </xsl:element>

      <CustomerNumber>
        <xsl:value-of select="CustomerID"/>
      </CustomerNumber>
      <OrderLines>
        <xsl:for-each select="ancestor::*/Orders[OrderID = $OrderID]">
          <ProductID>
            <xsl:value-of select="ProductID"/>
           </ProductID>
        </xsl:for-each>
      </OrderLines>
    </Order>

  </xsl:template>

</xsl:stylesheet>

Thanks in advance

May the source be with you

//seesharper

It's a viable approach, but not very efficient. As a simple improvement, you could replace the use of the "preceding" axis with preceding-sibling.

The problem you are tackling is generally called "grouping", and there is a whole literature on the subject. Start with http://www.jenitennison.com/xslt/grouping. Grouping using keys (Muenchian grouping) is hard to understand at first but much more efficient for large files. XSLT 2.0 has an <xsl:for-each-group> construct which makes this kind of problem very easy to code.

Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference

I will look into XSLT 2.0, but since the 2.0 .Net Framework don't support XSLT 2.0, I'm stuck with solutions like this.
Can u believe they didn't put that in, by the way?

Thanks a lot, mhkay