XRX/Autoincrement File ID
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[edit] Motivation
You want to create a new file and automatically create a new identifier for the file.
[edit] Method
Create an XML file with a single counter in it. Use this counter as part of the file name. After you confirm that the file has been saved, increment the counter using the update function.
[edit] Sample XML File to Hold Next ID
<data> <next-id>47</next-id> </data>
[edit] Sample Code for save-new.xq
The following example works with an incoming HTTP POST request.
xquery version "1.0";
declare namespace exist = "http://exist.sourceforge.net/NS/exist";
declare namespace xmldb = "http://exist-db.org/xquery/xmldb";
declare namespace request="http://exist-db.org/xquery/request";
declare option exist:serialize "method=html media-type=text/html indent=yes";
(: save a new task - filename: save-new.xq - change base path if this changes. :)
(: this only works with POST data :)
let $my-doc := request:get-data()
(: the base directory URL for this XQuery. Use this to put links in the result page. :)
let $base-path := substring-before(request:get-url(), '/save-new.xq')
(: these paths must start with '/db' and are used for passing to doc() :)
let $data-collection := '/db/app/data'
let $next-id-file-path := '/db/app/edit/next-id.xml'
let $next-id := doc($next-id-file-path)/data/next-id/text()
(: use this as an arugment for for store command :)
let $new-term-base-file-name := concat($next-id, '.xml')
(: use this for doc :)
let $new-term-file-path := concat($data-collection, '/', $new-term-base-file-name)
(: add this line for testing in your local system or if you don't have group or RBAC set up :)
let $login := xmldb:collection($data-collection, 'mylogin', 'mypassword')
(: store the new document in the given collction :)
let $store-return-status := xmldb:store($data-collection, $new-term-base-file-name, $my-doc)
(: increment the next-id by one for the next document. You can also use "update value" :)
let $retCode1 := update replace doc($next-id-file-path)/data/next-id/text()
with ($next-id + 1)
(: note that next-id is now the next item so the current is next-id -1 :)
(: update the ID in the new document. Note that the saved document must have
the ID in the path /app/id. :)
let $retCode2 := update replace doc($new-term-file-path)/app/id with <id>{$next-id - 1}</id>
return
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Save Confirmation</title>
</head>
<body>
<h1>New file has been saved. id={$next-id - 1}.</h1>
</body>
</html>
[edit] Taking into account concurrent access
Same as above but with locking the node holding the identifier.
The following example works with an incoming HTTP POST request.
xquery version "1.0";
declare namespace exist = "http://exist.sourceforge.net/NS/exist";
declare namespace xmldb = "http://exist-db.org/xquery/xmldb";
declare namespace request="http://exist-db.org/xquery/request";
declare option exist:serialize "method=html media-type=text/html indent=yes";
(: save a new task - filename: save-new.xq - change base path if this changes. :)
(: this only works with POST data :)
let $my-doc := request:get-data()
(: the base directory URL for this XQuery. Use this to put links in the result page. :)
let $base-path := substring-before(request:get-url(), '/save-new.xq')
(: these paths must start with '/db' and are used for passing to doc() :)
let $data-collection := '/db/app/data'
let $next-id-file-path := '/db/app/edit/next-id.xml'
(: Get next-id current value and increment the node value with an exclusive lock of the node :)
let $next-id := util:exclusive-lock(
doc($next-id-file-path)/data/next-id,
let $current-id := doc($next-id-file-path)/data/next-id/text()
let $retCode := update replace doc($next-id-file-path)/data/next-id/text() with ($current-id + 1)
return ($current-id - 1))
(: Warning - Pitfall : $current-id evaluation changes after the update :)
(: use this as an arugment for for store command :)
let $new-term-base-file-name := concat($next-id, '.xml')
(: use this for doc :)
let $new-term-file-path := concat($data-collection, '/', $new-term-base-file-name)
(: add this line for testing in your local system or if you don't have group or RBAC set up :)
let $login := xmldb:collection($data-collection, 'mylogin', 'mypassword')
(: store the new document in the given collction :)
let $store-return-status := xmldb:store($data-collection, $new-term-base-file-name, $my-doc)
(: update the ID in the new document. Note that the saved document must have
the ID in the path /app/id. :)
let $retCode2 := update replace doc($new-term-file-path)/app/id with <id>{$next-id}</id>
return
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Save Confirmation</title>
</head>
<body>
<h1>New file has been saved. id={$next-id}.</h1>
</body>
</html>
[edit] Adding and Incrementing an Attribute
Note that the syntax for inserting an attribute is the following:
update insert attribute {$attrName} {$attrValue} into expression
The keyword attribute must be used and be followed with the attribute name and value.
If you want to store a new id in an attribute the syntax is:
update insert attribute {'id'} {$next-id} into $doc/root
Note: if the attribute already exists in the target node then insert works as replace
And if you are updating the id you can use the replace function with the @ in the path expression:
update replace doc/root/@id with ($next-id + 1)
