Re: [xsl] variable scope

Subject: Re: [xsl] variable scope
From: "G. Ken Holman" <gkholman@xxxxxxxxxxxxxxxxxxxx>
Date: Thu, 21 Aug 2008 22:25:31 -0400
At 2008-08-21 19:12 -0500, Greg Fausak wrote:
I've got a situation where an attribute may or
may not be set.  I'm building a postgres ddl from xml source that looks like:

...
<views>
  <view name="super.av_address" source="super"/>
  <view name="brand.av_address" source="brand"/>
  <view name="av_address" source="agentviaconsumer" schema="agent" />
  <view name="av_address" source="consumer" schema="consumer"/>
  <view name="av_address" source="fast_consumer" schema="fast_consumer"/>
</views>
...

(Warning: I am going to use the term 'schema' in a postgres relational
context in
this paragraph, not the xml context!).  Sometimes I have a view name which
contains the schema in the name attribute, like the first two above.
Then sometimes
I have the schema defined in the schema attribute, like the last
three.  It's easy enough
to get the data from the attributes into variables sname and vname like:

        <xsl:for-each select="//views/view">
                <xsl:choose>
                        <xsl:when test="@source = 'super'">
                                <xsl:choose>
                                        <xsl:when test="@schema">
                                                <xsl:variable
name="sname" select="@schema"/>
                                                <xsl:variable
name="vname" select="@name"/>
                                                <xsl:variable
name="tname" select="str:replace($vname,'av_','at_')"/>
                                                <xsl:call-template
name="create-super-view">

<xsl:with-param name="schemaname" select="$sname"/>

<xsl:with-param name="viewname" select="$vname"/>

<xsl:with-param name="tablename" select="$tname"/>
                                                </xsl:call-template>

The above can be written much more simply as:


<xsl:call-template name="create-super-view">
  <xsl:with-param name="schemaname" select="@schema"/>
  <xsl:with-param name="viewname" select="@name"/>
  <xsl:with-param name="tablename" select="str:replace($vname,'av_','at_')"/>
</xsl:call-template>

... because there is no obligation to use variables.

However, it would be so much more readable if I could do the variable assignment one time, something like:

Then you will have to turn the assignment inside out, because the scope of local variables is the following siblings and their descendants. By "turning it inside out", I'm saying that you have to put the choosing on the value assigned, rather than on the assignment itself:


<xsl:variable name="sname">
  <xsl:choose>
    <xsl:when....
</xsl:variable>
<xsl:variable name="vname">
  <xsl:choose>
    <xsl:when...
</xsl:variable>

.... and then the variables are in scope for later use.

But I think you are taking too much of a "programmer's perspective" on the constructs available in XSLT and you probably can get away without any (or many) of the variables you've shown in your snippet.

I hope this helps.

. . . . . . . . . Ken


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