I believe this could be fixed (if necessary) by wrapping the current-dateTime()
call with a xdmp:eval.
xdmp:eval("current-dateTime()")
Darin.
-----Original Message-----
From: [email protected] on behalf of Geert Josten
Sent: Mon 3/29/2010 10:00 AM
To: General Mark Logic Developer Discussion
Subject: RE: [MarkLogic Dev General] Unique key construction
Note: this code will return only one unique value per transaction.
current-datetime() returns the same value throughout the transaction as
MarkLogic Server is based on point-in-time querying..
Kind regards,
Geert
________________________________
From: [email protected]
[mailto:[email protected]] On Behalf Of Keith L. Breinholt
Sent: maandag 29 maart 2010 16:45
To: General Mark Logic Developer Discussion
Subject: RE: [MarkLogic Dev General] Unique key construction
Here is a UUID version 3 implementation that we use for URLs that is unique to
the name, host and time created:
declare variable $g_defaultNamespace as xs:string :=
xdmp:host-name(xdmp:host());
declare variable $g_uuidVersion as xs:unsignedLong := 3;
declare variable $g_uuidReserved as xs:unsignedLong := 8;
(:
Calculate the UUID and set the UUID property on the file.
The layout of a UUID is as follows.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 a b c d e f 0 1 2 3 4 5 6 7 8 9 a b c d e f
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| time_low |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| time_mid | time_hi |version|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|clk_seq_hi |res| clk_seq_low | node (0-1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| node (2-5) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3 4 5 6 7 8 9 a b c d e f 0 1 2 3 4 5 6 7 8 9 a b c d e f
This implements version 3 of the UUID specification.
The timestamp is a 60-bit value.
The clock sequence is a 14 bit value.
The node is a 48-bit name value.
:)
declare function meta:uuid( $uri as xs:string )
as xs:string
{
meta:uuid( $uri, $g_defaultNamespace )
};
declare function meta:uuid( $uri as xs:string, $namespace as xs:string )
as xs:string
{
(: calculate md5 with a dateTime for our random values :)
let $hash := xdmp:md5( concat( $uri, xs:string(current-dateTime()),
$namespace ) )
return
concat (
substring( $hash, 1, 15 ),
(: set version bits :)
xdmp:integer-to-hex($g_uuidVersion),
(: set reserved bits :)
substring( $hash, 17, 1 ),
xdmp:integer-to-hex((xdmp:hex-to-integer(substring($hash, 18, 1)) idiv 4)
+ $g_uuidReserved),
substring( $hash, 19, 14 )
)
};
Keith L. Breinholt
[email protected]
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Geert Josten
Sent: Monday, March 29, 2010 2:35 AM
To: General Mark Logic Developer Discussion
Subject: RE: [MarkLogic Dev General] Unique key construction
Hi Deepak,
Look in the Modules, not the Admin folder. Here is a typical case taken from
triggers.xqy:
define function
get-unique-trigger-id()
as xs:unsignedLong
{
let $col := triggers-collection(),
$attempt := xdmp:random(),
$doc-uri := fn:concat(triggers-uri(), xs:string($attempt)),
$docs := for $d in fn:collection($col) return fn:base-uri($d)
return
if ($doc-uri = $docs)
then get-unique-trigger-id()
else $attempt
}
You can make it slightly more robust by counting the attempts and throwing an
error if you need to many attempts. The number of unique numbers generated by
xdmp:random is large though, so that is only necessary when you have good
reason to believe that you could approach that limit..
Kind regards,
Geert
>
drs. G.P.H. (Geert) Josten
Consultant
Daidalos BV
Hoekeindsehof 1-4
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> From: [email protected]
> [mailto:[email protected]] On Behalf Of
> deepak mohan
> Sent: zondag 28 maart 2010 17:44
> To: [email protected]
> Subject: [MarkLogic Dev General] Unique key construction
>
> Hi All,
>
> Please tell me how ML constructs the unique ID while creating
> any ML entities(App Servers, DB, forest etc.). I need to
> generate a unique ID. I tried dig into the ML Admin modules
> APi, I couldnot find the algo. Are they using random() and
> check for existence?
>
> Thanks,
> Deepak Mohanakrishnan.
>
>
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>
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