XSLT: How to remove elements of a resulting result tree fragment while copying? - xslt

Question

My goal is to extract the contents of the SOAP body, f.e. the ElementsToExtract node - but the node name can basically be arbitrary:
<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:soap="http://www.w3.org/2003/05/soap-envelope">
<soap:Header>
<MessageId>52DF2371-4094-4408-A3EA-42D73FD1B7A3</MessageId>
</soap:Header>
<soap:Body>
<ElementsToExtract>
...
<RemoveMe>...</RemoveMe>
<RemoveMeAlso>...</RemoveMeAlso>
...
</ElementsToExtract>
</soap:Body>
</soap:Envelope>
While I'm extracting the contents, I want to get rid of two elements that all my source documents have in common - say RemoveMe and RemoveMeAlso. As there's a chance that the deeper nested nodes may be called the same, they must only be stripped from the layer below the ElementsToExtract node. How would I formulate that expression?
Here's what I did up to now:
<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:soap="http://www.w3.org/2003/05/soap-envelope"
xmlns:exsl="http://exslt.org/common"
exclude-result-prefixes="soap exsl">
<xsl:output method="xml" indent="yes" omit-xml-declaration="no"/>
<xsl:strip-space elements="*"/>
<xsl:variable name="SoapHeaderContents" select="exsl:node-set(soap:Envelope/soap:Header/*)"/>
<xsl:variable name="SoapBodyContents" select="exsl:node-set(soap:Envelope/soap:Body/*)"/>
<xsl:template match="#*|node()">
<xsl:copy>
<xsl:apply-templates select="#*|node()"/>
</xsl:copy>
</xsl:template>
<xsl:template match="/">
<xsl:apply-templates select="$SoapBodyContents"/>
</xsl:template>
<!-- This is global, how to restrict to the ElementsToExtract element? -->
<xsl:template match="node()[name() = 'RemoveMe']"/>
<xsl:template match="node()[name() = 'RemoveMeAlso']"/>
</xsl:stylesheet>
I also played with the node-set() function, having read that one can not modify result tree fragments (they're only text nodes?), but I don't quite understand how to address the resulting nodes of that set. So the nodes weren't removed:
<xsl:template match="/">
<xsl:apply-templates select="$SoapBodyContents"/>
<xsl:apply-templates select="$SoapBodyContents/RemoveMe" mode="m1"/>
</xsl:template>
<xsl:template name="StripRemoveMe" match="RemoveMe" mode="m1"/>
I also read some parts of the specification, but to no avail. I'm lost for clues. Can someone direct me to the right approach?

Answer 1

Would this work for you:
XSLT 1.0
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:soap="http://www.w3.org/2003/05/soap-envelope"
exclude-result-prefixes="soap">
<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>
<xsl:strip-space elements="*"/>
<!-- identity transform -->
<xsl:template match="#*|node()">
<xsl:copy>
<xsl:apply-templates select="#*|node()"/>
</xsl:copy>
</xsl:template>
<!-- skip soap wrappers -->
<xsl:template match="/soap:Envelope">
<xsl:apply-templates select="soap:Body/ElementsToExtract"/>
</xsl:template>
<!-- remove unwanted elements -->
<xsl:template match="ElementsToExtract/RemoveMe | ElementsToExtract/RemoveMeAlso"/>
</xsl:stylesheet>
In the (unlikely) case you don't know the name of the ElementsToExtract element, you could use:
<!-- skip soap wrappers -->
<xsl:template match="/soap:Envelope">
<xsl:apply-templates select="soap:Body/*"/>
</xsl:template>
<!-- remove unwanted elements -->
<xsl:template match="soap:Body/*/RemoveMe | soap:Body/*/RemoveMeAlso"/>

Answer 2

Some quick thoughts.
You create variables for storing the SOAP header and body. These are already in the input document, so it makes more sense to just write templates that match these.
Although you create a variable for the SOAP header, you never use it anywhere.
If you try to apply templates in succession, as in your sample XSL code, you will get all the output nodes from the first apply-templates, and then all the output nodes from the next apply-templates. If these nodes are meant to be interleaved in any way, this approach will not produce viable output.
Here's a revised version of your sample input XML, adding in a couple elements that we want to keep.
<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:soap="http://www.w3.org/2003/05/soap-envelope">
<soap:Header>
<MessageId>52DF2371-4094-4408-A3EA-42D73FD1B7A3</MessageId>
</soap:Header>
<soap:Body>
<ElementsToExtract>
<KeepMe>This text will persist in the output.</KeepMe>
<RemoveMe>This is text that will be removed.</RemoveMe>
<RemoveMeAlso>This will also vanish from the output.</RemoveMeAlso>
<OtherElementToKeep>And this one will also be kept.</OtherElementToKeep>
</ElementsToExtract>
</soap:Body>
</soap:Envelope>
Here's what we'd want as output:
<?xml version="1.0" encoding="utf-8"?>
<ElementsToExtract>
<KeepMe>This text will persist in the output.</KeepMe>
<OtherElementToKeep>And this one will also be kept.</OtherElementToKeep>
</ElementsToExtract>
This XSL 1.0 code will do the job. I'm guessing from your post that you're not familiar with XSL processing flow, so I've added comments to help explain what's going on.
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:soap="http://www.w3.org/2003/05/soap-envelope"
version="1.0"
exclude-result-prefixes="soap">
<xsl:strip-space elements="*"/>
<xsl:output method="xml" indent="yes"/>
<!-- The `/` matches the _logical root_ of the input file. This is
basically equivalent to the start of the file, NOT the first element.
This is a common place to start processing in XSL. -->
<xsl:template match="/">
<!-- We just apply templates. In your case, we know already that
we DON'T want to process everything: we want to leave certain
things out, including a lot of the outermost elements. So
we specify what to target in the `select` statement. -->
<xsl:apply-templates select="soap:Envelope/soap:Body/ElementsToExtract"/>
</xsl:template>
<!-- This is the "identity" template, so called because it
just copies over applicable matches identically.
A template with a more-specific match statement takes
precedence. -->
<xsl:template match="#*|node()">
<xsl:copy>
<xsl:apply-templates select="#*|node()"/>
</xsl:copy>
</xsl:template>
<!-- Here, we specify exactly those elements that are in the
processing flow, and that we want to exclude from the
output. Since `soap:Header` etc. are NOT in the processing
flow (their element trees were never included in a preceding
call to `apply-templates`), we don't need to worry about those. -->
<xsl:template match="RemoveMe | RemoveMeAlso"/>
</xsl:stylesheet>
Note that the outermost element in the output is ElementsToExtract. This element will include the xmlns:soap="http://www.w3.org/2003/05/soap-envelope" namespace declaration, even though this namespace isn't used in any of the output elements (at least, for this small sample input XML).
If you can use XSL 2.0+ and you want to remove this namespace from the output, you could add the copy-namespaces="no" attribute to the <xsl:copy> element.