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:unpath
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
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