Simple XSLT Attribute Addition

I'm looking to do some really simply XSLT on my XML document, which has a structure like:

<XML>
    <TAG1 attribute1="A">
        <IRRELEVANT />
        <TAG2 attribute2="B" attribute3="34" />
    </TAG1>
</XML>

And am trying to make a XSLT which does the following:

1. Copy everything
2. If TAG2@attribute1="A" AND TAG2@attribute2="B" AND there is no TAG2@attribute4, then add @attribute4 to TAG2 and have its value to be the value of TAG2@attribute3

My unsuccessful attempt is below. The error I'm getting is "xsl:attribute: Cannot add attributes to an element if children have been already added to the element."

Thanks!

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0"  
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:param name="newDocumentHeader" />

   <!-- copy idiom copying ALL nodes -->
   <xsl:template match="node()|@*">
      <xsl:copy>
         <xsl:apply-templates select="node() | @*" />
   开发者_JS百科   </xsl:copy>
   </xsl:template>

   <!-- override for special case -->
   <xsl:template match="TAG1[@attribute1='A']/TAG2[@attribute2='B'][not(@attribute4)]">
        <xsl:attribute name="attribute4">
        <xsl:value-of select="@attribute3" />
        </xsl:attribute>
    </xsl:template>

</xsl:stylesheet>

<xsl:stylesheet version="1.0"
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

    <xsl:template match="node() | @*">
        <xsl:copy>
            <xsl:apply-templates select="node() | @*" />
        </xsl:copy>
    </xsl:template>

    <xsl:template match="TAG1[@attribute1 = 'A']/TAG2[@attribute2= 'B' ][not(@attribute4)]">
        <xsl:copy>
            <xsl:attribute name="attribute4">
                <xsl:value-of select="@attribute3" />
            </xsl:attribute>
            <xsl:apply-templates  select="node() | @*"/>
        </xsl:copy>

    </xsl:template>

</xsl:stylesheet>

Result:

<XML>
    <TAG1 attribute1="A">
        <IRRELEVANT />
        <TAG2 attribute4="34" attribute2="B" attribute3="34" />
    </TAG1>
</XML>

What is missing in your XSLT code is just the copy of the matched element. However, in your case (Simple XSLT Attribute Addition) you can override directly attribute3 node:

<xsl:template match="TAG1[@attribute1='A']
         /TAG2[@attribute2='B' and not(@attribute4)]
          /@attribute3">
    <xsl:copy-of select="."/>
    <xsl:attribute name="attribute4">
        <xsl:value-of select="." />
    </xsl:attribute>
</xsl:template>

Integrated in your current transform, produces:

<XML>
    <TAG1 attribute1="A">
        <IRRELEVANT></IRRELEVANT>
        <TAG2 attribute2="B" attribute3="34" attribute4="34"></TAG2>
    </TAG1>
</XML>