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
2665 JZ Bleiswijk
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F +31 (0)10 850 1199
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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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