Hi Eric, If you are willing to add identifying attributes anyway, why not use simple integer based values, allowing use of expressions like max(//@id) + 1 to calculate the next id value? Or if you need to calculate multiple values in one pass: max(//@id) + count(preceding-sibling::*) + 1..
Kind regards, Geert > Drs. G.P.H. Josten Consultant http://www.daidalos.nl/ Daidalos BV Source of Innovation Hoekeindsehof 1-4 2665 JZ Bleiswijk Tel.: +31 (0) 10 850 1200 Fax: +31 (0) 10 850 1199 http://www.daidalos.nl/ KvK 27164984 De informatie - verzonden in of met dit emailbericht - is afkomstig van Daidalos BV en is uitsluitend bestemd voor de geadresseerde. Indien u dit bericht onbedoeld hebt ontvangen, verzoeken wij u het te verwijderen. Aan dit bericht kunnen geen rechten worden ontleend. > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of > Eric Palmitesta > Sent: dinsdag 14 oktober 2008 16:48 > To: General Mark Logic Developer Discussion > Subject: Re: [MarkLogic Dev General] xpath string construction > > Hi Wayne, > > Yes, I've been looking into generating unique identifiers to > ease such things as deletion. I'm still new to the > 'document' model, still figuring out what's portable from my > 'relational' model experience. > > Is xdmp:request() guaranteed to be unique? If so, that's a > candidate to use as a unique identifier when inserting a new node. > > If there's a way to synchronize a particular block of code > across all sessions across all e-nodes, a hash of > xdmp:request-timestamp() might also work. > > I'm sure some mailing-list-folk have needed to generate an > identifier which is guaranteed unique, anyone have > suggestions / advice? > > Much thanks, > > Eric > > Wayne Feick wrote: > > Hi Eric, > > > > In 4.0, you can use xdmp:unpath() to do this > > > > > > > http://developer.marklogic.com/pubs/4.0/apidocs/Extension.html#xdmp:un > > path > > > > However, in the example you've given I'd recommend changing the > > approach to use some sort of an id attribute on person (since there > > are duplicate > > names) rather than a positional XPath expression. With your current > > approach, two users could each intend to delete "bob" at > index 3 when > > in fact the second attempt would actually delete "ryan". > > > > As a rule, exposing xpath expressions to a web app is > dangerous since > > there is no guarantee they still refer to the same node from one > > transaction to the next. > > > > Wayne. > > > > > > On Fri, 2008-10-10 at 14:43 -0400, Eric Palmitesta wrote: > >> Is there a specific reason why one can't construct an > xpath out of a string? > >> > >> For example, > >> > >> let $media := 'book' (: or 'journal', or 'article' :) return > >> doc('/path/to/file.xml')/path/to/$media/title > >> > >> Another use case, I want to display a list of items, and offer a > >> 'delete' link for each item. > >> > >> lets say /people.xml contained the following: > >> <people> > >> <person name="bob" /> > >> <person name="jim" /> > >> <person name="bob" /> > >> <person name="ryan" /> > >> </people> > >> > >> So I'd display something like: > >> > >> for $person in doc('/people.xml')/people/person return > >> <div> > >> $person/@name > >> <a href="delete.xqy?path={ xdmp:path($person) }>delete</a> > >> </div> > >> > >> This will give me nice delete links like > >> "delete.xqy?path=/people/person[1]", but in the supposed > delete.xqy, > >> I'd want to do something similar to: > >> > >> let $file := '/people.xml' > >> let $person := xdmp:get-request-field('path') return > >> xdmp:node-delete(doc($file)/$person) > >> > >> I can't, of course, the doc call will be fine but I can't > construct > >> xpath with a string. And the node-delete (and any other > >> node-manipulation function) requires actual nodes, not strings. > >> > >> I end up having to write eval-based utility functions: > >> > >> define function util:remove-element($uri as xs:string, $xpath as > >> xs:string) { > >> let $node := concat("doc('", $uri, "')", $xpath) > >> return > >> xdmp:eval(concat("xdmp:node-delete(", $node, ")")) } > >> > >> Please tell me I'm all wrong and there's a better way. > >> > >> Cheers, > >> > >> Eric > >> _______________________________________________ > >> General mailing list > >> General@developer.marklogic.com > >> <mailto:General@developer.marklogic.com> > >> http://xqzone.com/mailman/listinfo/general > > > > > ---------------------------------------------------------------------- > > -- > > > > _______________________________________________ > > General mailing list > > General@developer.marklogic.com > > http://xqzone.com/mailman/listinfo/general > _______________________________________________ > General mailing list > General@developer.marklogic.com > http://xqzone.com/mailman/listinfo/general > _______________________________________________ General mailing list General@developer.marklogic.com http://xqzone.com/mailman/listinfo/general
