[xquery-talk] Help understanding typeswitch-based Identity Transform

[Bridger Dyson-Smith]

Hi Joe,

thanks for the response. I'll explore moving the XPath checks and see where
that gets me.

Appreciatively,
Bridger


On Fri, Feb 16, 2018 at 11:01 AM, Joe Wicentowski <joewiz at gmail.com> wrote:

> Hi Bridger,
>
> To be able to treat your field elements differently based on their @name,
> you'd have to add some conditional logic to the return clause of your
> "element(field)" case.  You could place this logic right in local:dispatch,
> or you could create a new function, like local:field, which would take a
> field element and check the value of @name.
>
> You're right that typeswitch is limited to relatively simple sequence
> patterns, and doesn't accommodate full XPath expressions.  Typically,
> typeswitch performs the high level node type or element name check, and
> then delegates more complex logic to functions.
>
> Joe
>
> On Thu, Feb 15, 2018 at 12:04 PM, Bridger Dyson-Smith <
> bdysonsmith at gmail.com> wrote:
>
>> Hi list --
>>
>> I'm trying to get a better understanding of identity transforms in Xquery
>> and I don't understand the finer points of the approaches for dealing with
>> specific elements.
>>
>> I've finally to become used to the XSLT approach, using a matching
>> template to process `field[@name='first']`, e.g. would someone be willing
>> to shine some light on different methods for dealing with this?
>>
>> Thanks very much for your time and trouble.
>> Best,
>> Bridger
>>
>> Example:
>>
>> declare variable $input :=
>>   <docs>
>>     <doc>
>>       <title>ABC: The Alphabet</title>
>>       <author>Some Person</author>
>>       <fields>
>>         <field name="first">First Field</field>
>>         <field name="second">Second Field</field>
>>       </fields>
>>     </doc>
>>   </docs>;
>>
>> declare function local:passthru( $node as node()* ){
>>   local:dispatch($node/node())
>> };
>>
>> declare function local:dispatch(
>>   $nodes as node()*
>> ) as item()* {
>>   for $node in $nodes
>>   return
>>     typeswitch($node)
>>       case text() return $node
>>       case element(docs) return local:passthru($node)
>>       case element(doc) return local:docf($node)
>>       case element(title) return local:title($node)
>>       case element(author) return local:author($node)
>>       case element(fields) return local:passthru($node)
>>       case element(field) return () (:return empty sequence:)
>>       default return local:passthru($node)
>> };
>>
>> declare function local:docf($node) {
>>   <new>{local:dispatch($node/node())}</new>
>> };
>>
>> declare function local:title($node) {
>>   <new-title>{local:dispatch($node/node())}</new-title>
>> };
>>
>> declare function local:author($node) {
>>   <new-author>{local:dispatch($node/node())}</new-author>
>> };
>>
>> local:dispatch($input)
>>
>> Output should look something like:
>>
>> <new>
>>   <new-title>ABC: The Alphabet</new-title>
>>   <new-author>Some Person</new-author>
>>   <new-subject>First Field</new-subject>
>>   <new-section>
>>     <new-entry>Second Field</new-entry>
>>   </new-section>
>> </new>
>>
>>
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>>
>
>
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