You should use a template that is only applied when the specified field is there. These templates in xslt are applied automatically only if the field is there:

<xsl:template match="doc:metadata/doc:element[@name='dc']/doc:element[@name='publication']/doc:element[@name='volume']/doc:element/doc:field[@name='value']">
  <xsl:text>Vol. </xsl:text
 <xsl:apply-templates/>
</xsl:template>

If the field is defined, but empty you should do:

<xsl:template match="doc:metadata/doc:element[@name='dc']/doc:element[@name='publication']/doc:element[@name='volume']/doc:element/doc:field[@name='value']">
  <xsl:if test="not(.='')">
     <xsl:text>Vol. </xsl:text
     <xsl:apply-templates/>
  </xsl:if>
</xsl:template>

Xslt is not a procedural language, you should hardly ever use <xsl:for-each>

Peter


-----Original Message-----
From: Code for Libraries [mailto:[log in to unmask]] On Behalf Of Matt Sherman
Sent: dinsdag 2 juni 2015 21:35
To: [log in to unmask]
Subject: Re: [CODE4LIB] XSLT Advice

Cool.  I talked to Ron via phone so I am getting a better picture, but I am still happy to take more insights.

So the larger context.  I inherited a DSpace instance with three custom metadata fields which actually have some useful publication information, though they improperly titled them in by associating them with a dc prefix but there were two many to fix quickly and they haven't broken DSpace yet so we continue.  So I added to the XSL to pull the data within the the custom fields to display "publication name" Vol. "publication volume" Issue "publication issue".  That worked really well until I realized that there was no conditional so even when the fields are empty I still get: <dc:identifier>Vol.
Issue</dc:identifier>

So here are the Custom Metadata fields:

dc.publication.issue
dc.publication.name
dc.publication.volume


Here is the customized XSLT, with dc.identifier added for context of what the rest of the sheet looks like.

<!-- dc.identifier -->
            <xsl:for-each
select="doc:metadata/doc:element[@name='dc']/doc:element[@name='identifier']/doc:element/doc:field[@name='value']">
                <dc:identifier><xsl:value-of select="." /></dc:identifier>
            </xsl:for-each>

<!-- dc.identifier.* -->
<xsl:for-each select="doc:metadata/doc:element[@name='dc']/doc:element[@name='identifier']/doc:element/doc:element/doc:field[@name='value']">
                <dc:identifier><xsl:value-of select="." /></dc:identifier> </xsl:for-each>

<!-- dc.publication fields to dc.identifier --> <dc:identifier><xsl:value-of select="doc:metadata/doc:element[@name='dc']/doc:element[@name='publication']/doc:element[@name='name']/doc:element/doc:field[@name='value']"/><xsl:text>
Vol. </xsl:text><xsl:value-of
select="doc:metadata/doc:element[@name='dc']/doc:element[@name='publication']/doc:element[@name='volume']/doc:element/doc:field[@name='value']"/><xsl:text>
Issue </xsl:text><xsl:value-of
select="doc:metadata/doc:element[@name='dc']/doc:element[@name='publication']/doc:element[@name='issue']/doc:element/doc:field[@name='value']"/></dc:identifier>


Ron suggested that using choose and when and that does seem to make the most sense.  The other trickiness is that I have found that some of these fields as filled when others are blank, such as their being a volume but not an issue.  So I need to figure out how to test multiple fields so that I can have it display differently dependent on what has data or not at all none of the fields are filled, which is the case in items such as posters.

So any thoughts would help.  Thanks.

On Tue, Jun 2, 2015 at 2:50 PM, Wick, Ryan <[log in to unmask]> wrote:
> I agree with Stuart, post the example here.
>
> Or if you want more real-time chat there's always #code4lib IRC.
>
> For an XSLT resource, Dave Pawson's site is great: 
> http://www.dpawson.co.uk/xsl/sect2/sect21.html
>
> Ryan Wick
>
> -----Original Message-----
> From: Code for Libraries [mailto:[log in to unmask]] On Behalf 
> Of Stuart A. Yeates
> Sent: Tuesday, June 02, 2015 11:46 AM
> To: [log in to unmask]
> Subject: Re: [CODE4LIB] XSLT Advice
>
> There are a number of experienced xslt'ers here. Post your example to the group so we can all learn.
>
> Cheers
> Stuart
>
> On Wednesday, June 3, 2015, Matt Sherman <[log in to unmask]> wrote:
>
>> Hi all,
>>
>> I am making a few corrections on an oai_dc.xslt file for our DSpace 
>> instance I slightly botched modifying to integrate some custom 
>> metadata into a dc.identifier citation in the OAI-PMH harvest.  I 
>> need to get proper conditionals so it can display and harvest the 
>> metadata correctly and not run when there is no data in those fields.  
>> I have a pretty good idea what I need to do, and if this were like 
>> JavaScript or Python I could probably muddle through.  The trouble is 
>> that I don't know the conditional syntax for XSLT quite well enough 
>> to know what I can do and thus need to do.  Plus the online resources 
>> for learning/referencing XSLT for this are a bit shallow for what I 
>> need hence asking the group.  So if there is anyone who knows XSLT 
>> really well that would be willing to talk with me for a bit to help 
>> me work through what I need to get the syntax to work like I want I 
>> would appreciate it.  Thanks.
>>
>> Matt Sherman
>>
>
>
> --
> --
> ...let us be heard from red core to black sky