Difference between revisions of "Update Module"

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Revision as of 13:13, 24 May 2018

This XQuery Module provides additional functions for performing updates and returning results in updating expressions.


All functions in this module are assigned to the http://basex.org/modules/update namespace, which is statically bound to the update prefix.

Except for update:output-cache, all functions are updating and thus comply to the XQuery Update constraints.



Signatures update:apply($function as function(*), $arguments as array(*))) as empty-sequence()
Summary The updating variant of fn:apply applies the specified updating $function to the specified $arguments.
  • Creates a new database with an initial document and adds a document to an existing database.
declare %updating function local:update(
  $database  as xs:string,
  $path      as xs:string,
  $function  as %updating function(item(), xs:string) as empty-sequence()
) as empty-sequence() {
  update:apply($function, [ $database, $path ])
local:update('new-db', 'doc.xml', db:create#2),
local:update('existing-db', 'doc.xml', db:add#2)


Signatures update:for-each($seq as item()*, $function as function(item()) as item()*)) as empty-sequence()
Summary The updating variant of fn:for-each applies the specified updating $function to every item of $seq.
  • Creates two databases:
let $names := ('db1', 'db2')
return update:for-each($names, db:create#1)


Signatures update:for-each-pair($seq1 as item()*, $function as function(item()) as item()*)) as empty-sequence()
Summary The updating variant of fn:for-each-pair applies the specified updating $function to the successive pairs of items of $seq1 and $seq2. Evaluation is stopped if one sequence yields no more items.
  • Renames nodes in an XML snippets:
copy $xml := <xml><a/><b/></xml>
modify update:for-each-pair(
  ('a', 'b'),
  ('d', 'e'),
  function($source, $target) {
    for $e in $xml/*[name() = $source]
    return rename node $e as $target
return $xml


Signatures update:map-for-each($map as map(*), $function as function(xs:anyAtomicType, item()*) as item()*) as item()*
Summary The updating variant of map:for-each applies the specified $function to every key/value pair of the supplied $map and returns the results as a sequence.
  • Inserts attributes into a document:
copy $doc := <xml/>
modify update:map-for-each(
  map {
    'id': 'id0',
    'value': 456
  function($key, $value) {
    insert node attribute { $key } { $value } into $doc
return $doc



Signatures update:output($result as item()*) as empty-sequence()
Summary This function is a helper function for returning results in an updating expression. The argument of the function will be evaluated, and the resulting items will be cached and returned after the updates on the pending update list have been processed. As nodes may be updated, they will be copied before being cached.
  • update:output("Prices have been deleted."), delete node //price deletes all price elements in a database and returns an info message.


Signatures update:output-cache() as item()*
Summary Returns the items that have been cached by update:output. It can be used to check which items will eventually be returned as result of an updating function.
This function is non-deterministic: It will return different results before and after items have been cached. It is e. g. useful when writing unit tests.


This module was introduced with Version 9.0.