Update Module

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

Conventions[edit]

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.

Updates[edit]

update:apply[edit]

Signature
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.
Examples
  • 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)

update:for-each[edit]

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

update:for-each-pair[edit]

Signature
update:for-each-pair(
  $input1  as item()*,
  $input2  as item()*,
  $action  as function(item()) as item()*
) as empty-sequence()
Summary The updating variant of fn:for-each-pair applies the specified updating $action to the successive pairs of items of $input1 and $input2. Evaluation is stopped if one sequence yields no more items.
Examples
  • 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

update:map-for-each[edit]

Signature
update:map-for-each(
  $map     as map(*),
  $action  as function(xs:anyAtomicType, item()*) as item()*
) as item()*
Summary The updating variant of map:for-each applies the specified $action to every key/value pair of the supplied $map and returns the results as a sequence.
Examples
  • 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

Output[edit]

update:output[edit]

Signature
update:output(
  $input  as item()*
) as empty-sequence()
Summary This function can be used if MIXUPDATES is not enabled, and if values need to be returned within an updating expression: The supplied $input will be cached and returned at the very end, i.e., after all updates on the pending update list have been processed. If one of the supplied items is affected by an update, a copy will be created and cached instead.
Examples
  • update:output("Prices have been deleted."), delete node //price deletes all price elements in a database and returns an info message.

update:cache[edit]

Signature
update:cache(
  $reset  as xs:boolean?  := false()
) as item()*
Summary Returns the items that have been cached by update:output. The output cache can optionally be $reset. The function can be used to check which items will eventually be returned as the result of an updating function.
This function is nondeterministic: It will return different results before and after items have been cached. The function can be useful for writing unit tests.

Changelog[edit]

Version 9.3
Version 9.1
  • update:output: Maps and arrays can be cached if they contain no persistent database nodes or function items.
Version 9.0

This module was introduced with Version 9.0.