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

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

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