Update Module

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

Contents

[edit] Conventions

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.

[edit] Updates

[edit] update:apply

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.
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)

[edit] update:for-each

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.
Examples
  • Creates two databases:
let $names := ('db1', 'db2')
return update:for-each($names, db:create#1)

[edit] update:for-each-pair

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.
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

[edit] update:map-for-each

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.
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

[edit] Output

[edit] update:output

Updated with Version 9.1: Maps and arrays can be cached if they contain no persistent database nodes or function items.

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. If the supplied item will be 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.

[edit] update:cache

Signatures update: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.

[edit] Changelog

Version 9.1
Version 9.0

This module was introduced with Version 9.0.

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