[MarkLogic Dev General] Unique key construction

Mon Mar 29 07:26:59 PST 2010

Correct, each unique URI passed in will have a different UUID.  But if you pass in the same URI in the same transaction it will return the same UUID.

Keith L. Breinholt
breinholtkl at ldschurch.org<mailto:breinholtkl at ldschurch.org>

From: general-bounces at developer.marklogic.com [mailto:general-bounces at developer.marklogic.com] On Behalf Of Geert Josten
Sent: Monday, March 29, 2010 9:00 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: general-bounces at developer.marklogic.com [mailto:general-bounces at developer.marklogic.com] 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

breinholtkl at ldschurch.org

-----Original Message-----
From: general-bounces at developer.marklogic.com [mailto:general-bounces at developer.marklogic.com] 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

2665 JZ Bleiswijk

T +31 (0)10 850 1200

F +31 (0)10 850 1199

mailto:geert.josten at daidalos.nl

http://www.daidalos.nl/

KvK 27164984

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> From: general-bounces at developer.marklogic.com

> [mailto:general-bounces at developer.marklogic.com] On Behalf Of

> deepak mohan

> Sent: zondag 28 maart 2010 17:44

> To: general at developer.marklogic.com

> 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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