Update Module

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==update:cache==
==update:cache==
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{{Mark|Updated with Version 9.3}}: {{code|$reset}} argument added.
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{{Mark|Updated with Version 9.3}}: {{code|$reset}} option added.
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Latest revision as of 12:40, 18 July 2019

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

Signatures update:output($items as item()*) as empty-sequence()
Summary This function can be used if MIXUPDATES is not enabled, and if values need to returned within an updating expression: The supplied $items 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.

[edit] update:cache

Updated with Version 9.3: $reset option added.

Signatures update:cache() as item()*
update:cache($reset as xs:boolean) 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 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 9.3
Version 9.1
Version 9.0

This module was introduced with Version 9.0.

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