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Re: dynamic xpath eval in xquery?

  • From: John Snelson <john.snelson@o...>
  • To: James Fuller <james.fuller.2007@g...>
  • Date: Tue, 09 Oct 2007 12:21:14 +0100

Re:  dynamic xpath eval in xquery?
Hi James,

There is no standard function in XQuery that will evaluate another 
XQuery stored in a string - although some XQuery implementations provide 
extension functions to do this.

Depending on your needs, it's not too hard to write your own function to 
handle simple cases, like this:

declare function local:evalPath($path as xs:string, $xml as node()*) as 
   local:evalPathImpl(tokenize($path, "/"), $xml)

declare function local:evalPathImpl($steps as xs:string*, $xml as 
node()*) as node()*
   if(empty($steps)) then $xml
   else if($steps[1] = "") then local:evalPathImpl(subsequence($steps, 
2), $xml/root())
   else if(starts-with($steps[1], "@")) then 
local:evalPathImpl(subsequence($steps, 2), $xml/@*[name() = 
substring($steps[1], 2)])
   else local:evalPathImpl(subsequence($steps, 2), $xml/*[name() = 

let $xml := document { <test><a><b attr="value"></b></a></test> }

let $xpathstring := "/test/a/b/@attr"

return local:evalPath($xpathstring, $xml)


James Fuller wrote:
> given in xquery v1.0
> let $xml := <test><a><b></b></a>
> let $xpathstring := ''test/a/b"
> return $xml/$xpathstring
> I know this is not possible ;) ... though I am having a brain cramp...
> wondering what the best approach for doing this type of thing in XQuery.
> tia, Jim Fuller
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John Snelson, Oracle Corporation
Berkeley DB XML:        http://www.oracle.com/database/berkeley-db/xml
XQilla:                                  http://xqilla.sourceforge.net

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