Question

I currently have an XML document like this:

<?xml version="1.0" encoding="ISO-8859-1"?>
<?xml-stylesheet type="text/xsl" href="./transform.xsl"?>
<Documentation><Tables>
<TABLE TABLE_NAME="FirstTable">
  <COLUMN COLUMN_NAME="FirstColumn" ORDINAL_POSITION="1" IS_NULLABLE="NO" DATA_TYPE="int" />
  <COLUMN COLUMN_NAME="SecondColumn" ORDINAL_POSITION="2" IS_NULLABLE="NO" DATA_TYPE="int" />
</TABLE>

...

</Tables><Comments>
<COMMENT ForTable="FirstTable" ForColumn="FirstColumn">Description of FirstColumn</COMMENT>
</Comments></Documentation>

My question is, how do I get the value of the COMMENT when looping over the tables and columns? I have:

<xsl:for-each select="//TABLE">
  ...
  <xsl:for-each select="COLUMN">
    ...
    <xsl:value-of select="//COMMENT[@ForTable = @TABLE_NAME and @ForColumn=@COLUMN_NAME]" />

But this doesn’t work. Any advice?

Answer 1

Another variant to solve this would be:

<xsl:for-each select="/Documentation/Tables/TABLE">
  <!-- select all comments for the current table name… -->
  <xsl:variable name="$comments" select="
    /Documentation/Comments/COMMENT[@ForTable = current()/@TABLE_NAME]
  "/>

  <xsl:for-each select="COLUMN">
    <!-- …of those, select the one with the current column name -->
    <xsl:value-of select="
      $comments[@ForColumn = current()/@COLUMN_NAME]
    " />
  </xsl:for-each>
</xsl:for-each>

The benefits are:

• you only need one variable, instead of two
• the inner for-each can run faster since it is looking at a smaller, pre-filtered data set

Note that:

• I use current() to refer to the XSLT context node within XPath predicates.
• I avoid // in XPath expressions, since it has really bad performance characteristics and should not be used if possible. Your input document structure implies that // is not necessary.