Re: [basex-talk] Determining if a node is a database node

5 Jul 2023

      Thanks for the tip.

A db:is-node() function would be most handy.

In my case, I’m using transform with to augment content pulled from the database before doing processing that will vary depending on whether I have a database node (i.e., getting its node ID or database path) or I don’t.

Of course it would also be useful for functions that may operate on database nodes or content parsed from the file system.

Cheers,

Eliot

_____________________________________________
Eliot Kimber
Sr Staff Content Engineer
O: 512 554 9368
M: 512 554 9368
servicenow.com<https://www.servicenow.com>
LinkedIn<https://www.linkedin.com/company/servicenow> | Twitter<https://twitter.com/servicenow> | YouTube<https://www.youtube.com/user/servicenowinc> | Facebook<https://www.facebook.com/servicenow>

From: Christian Grün <christian.gruen@gmail.com>
Date: Tuesday, July 4, 2023 at 4:14 AM
To: Eliot Kimber <eliot.kimber@servicenow.com>
Cc: basex-talk@mailman.uni-konstanz.de <basex-talk@mailman.uni-konstanz.de>
Subject: Re: [basex-talk] Determining if a node is a database node
[External Email]

Hi Eliot,

The XQuery Specification allows implementations to simplify an
expression if it always yields the same result in the case of success.
As db:node-id never returns an empty sequence, BaseX rewrites
exists(db:node-id()) to true().

You can use the following alternative:

declare function util:isDatabaseNode($node) {
  try {
    boolean(db:name($node))
  } catch db:node {
    false()
  }
};

It would be cleaner if we added a dedicated function for that in a
future version of BaseX.

Cheers,
Christian

On Mon, Jul 3, 2023 at 9:55 PM Eliot Kimber <eliot.kimber@servicenow.com> wrote:
...
I need to be able to determine if an arbitrary node is or is not a database node.
I implemented this function:
declare function util:isDatabaseNode($node as node()) as xs:boolean {
let $isDbNode as xs:boolean :=
try {
let $nodeId as xs:integer? := db:node-id($node)
(: let $msg := prof:dump(``[[DEBUG]   relpath:isDatabaseNode(): nodeId: "`{$nodeId}`"]``) :)
return exists($nodeId)
} catch * {
(: let $msg := prof:dump(``[[DEBUG]   relpath:isDatabaseNode(): Got exception `{$err:code}` - `{$err:description}`]``) :)
(: return :) false()
}
let $msg := prof:dump(``[[DEBUG]   relpath:isDatabaseNode(): Returning `{$isDbNode}``]``)
return $isDbNode
};
With the prof:dump() calls commented out as shown here, it always returns true, even when it returned false.
If I comment in the prof:dumps then I get the expected correct false result.
This must be the result some optimization at compile time but I haven’t been able to find a construction of this function that works without the debug messages.
Is there a better way to determine if a node is a database node?
This is with 10.6.
Cheers,
E.
_____________________________________________
Eliot Kimber
Sr Staff Content Engineer
O: 512 554 9368
M: 512 554 9368
servicenow.com
LinkedIn | Twitter | YouTube | Facebook