Hi Paul,
it should be all there in the documentation I linked to. I really don't know more than the documentation already says :) So to quote:
"Variables and context items can be declared via $bindings. The specified keys must be QNames or strings:
- If a key is a QName, it will be directly adopted as variable name. - It a key is a string, it may be prefixed with a dollar sign. Namespace can be specified using the Clark Notation. - If the specified string is empty, the value will be bound to the context item."
So the third bullet points applies here.
Cheers, Dirk
On 10/08/14 21:56, Paul Swennenhuis wrote:
Hi Dirk,
Cool! Exactly what I was looking for, and it executes fast as well. This is a life-saver for me.
Could you elaborate a bit on the "Using the empty string for the binding binds the element as context item (thus it must be a document)." remark? I'm not sure if I follow that... And what are the other binding options?
Thanks a lot.
Paul
Hi Paul,
xquery:eval() should be capable of doing what you want. Take a look at the first example at https://docs.basex.org/wiki/XQuery_Module
Using the empty string for the binding binds the element as context item (thus it must be a document). So the following should work for you:
xquery:eval($choice, map { '': document {$xml}})
Cheers, Dirk
On 10/08/14 21:15, Paul Swennenhuis wrote:
Suppose I have a variable $xml containing the XML fragment <places><village>Wismar</village><city>Amsterdam</city><village>Positano village, Italy</village><city>Prague</city></places> In a static world I would list all cities with the XPath expression $xml//city . And the villages with $xml//village .
OK. No issues. Runs fast.
Now suppose I want the user to decide whether to list either cities or villages. There are several ways to implement this, but I'm looking for the dynamic XPath solution.
Suppose the users choice ("city" or "village") resides in the string $choice Something like $xml/$choice abviously will not work. It will yield the string "village" or "city" 8 times (for all element and text nodes) xquery:eval() does not help either. xquery:eval($xml/$choice) is not valid, nor is $xml/xquery:eval($choice) or any variant of these, with or without parentheses or curly braces.
One way I have found to do it is like this:
xquery:eval(concat(fn:serialize($xml),$choice))
Complete query:
let $xml := <places><village>Wismar</village><city>Amsterdam</city><village>Positano village, Italy</village><city>Prague</city></places>
let $choice := '//village'
return xquery:eval(concat(fn:serialize($xml),$choice))
But obviously, this executes very slowly because the XML has to be serialized.
So is there any other way to do dynamic joining of XML fragments and XPath expressions given as string?
Oh, BTW, I am NOT looking for this solution: $xml//*[local-name()=$choice] Thiis may work for this case but not for other XPath expressions.