Best way to do dynamic XPath evaluation

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. > >

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. >>> >>> >

> 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. >> >>