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The {{Code|update}} expression is a convenience operator for the {{Code|copy/modify/return}} construct.
Similar to the [[XQuery 3.0#Simple Map Operator|XQuery 3.0 map operator]], the value of the first
expression is bound as context item, and the second expression performs updates on this item.
The updated item is returned as result.
With {{Version|8.5}}, the update expression was extended:
(<root1root/>, <root2/>) update {
The {{Code|<pre class="brush:xquery"><xml>text</xml> transform with}} expression is part { replace value of the [https://wwwnode .w3.org/TR/xquerywith 'new-update-30text'}</#id-transform-with XQuery Update 3.0]] working draft. It is also available in BaseX.pre>
Additional Numerous additional [[Database Module#Updates|database functions]] exist for performing updates on document and database level.
dbupdate:output("Update successful."), insert node <c/> into doc('factbook')/mondial
→Pending Update List
It summarizes the update features of BaseX.
BaseX offers a complete implementation of the[http://www.w3.org/TR/xquery-update-10/ XQuery Update Facility (XQUF)].This article aims to provide a very quick and basic introduction to the XQUF.First, some examples for update expressions are given. After that,a few problems the challenges are addressed that frequently arise due to the nature functional semantics of thelanguage. These are stated in the [[Update#Concepts|Concepts]] paragraph.
=Features=
==Non-Updating Expressions==
===transformcopy/modify/return===
<pre class="brush:xquery">
===update===
The {{Code|update}} expression is a BaseX-specific convenience operator for the {{Code|copy/modify/return}}
construct:
* Similar to the [[XQuery 3.0#Simple Map Operator|XQuery 3.0 map operator]], the value of the first
expression is bound as context item, and the second expression performs updates on this item.
The updated item is returned as result:
<pre class="brush:xquery">
return $item update delete node text()
</pre>
* More than one node can be specified as source:
</pre>
* In analogy with [[#transform with|transform with]], the updating expressions can – and should – be If wrapped with curly braces. * Update , update expressions can now be chained:
<pre class="brush:xquery">
insert node <child/> into .
} update {
===transform with===
The {{MarkCode|Introduced transform with Version 8.5}}expression was added to the current [https://www.w3.org/TR/xquery-update-30/#id-transform-with XQuery Update 3.0] working draft. It is a simple version of the [[#update|update]] expression and also available in BaseX:
==Functions==
===Built-in Functions===
{{Code|fn:put()}} is can be used to serialize XDM instances to secondary storage. It is : * The function will be executed at the end of a snapshotafter all other updates. * Serialized documents therefore reflect all changes made effective during a query.* No files will be created if the addressed nodes have been deleted.* Serialization parameters can be specified as third argument (more details are found in the [https://www.w3.org/TR/xquery-update-30/#id-func-put XQUF 3.0 Specification]).
===User-Defined Functions===
==Pending Update List==
The most important thing to keep in mind when using XQuery Update is the Pending Update List (PUL). Updating statements are not executed immediately, but are first collected as update primitives within a set-like structure. At After the end evaluation of a the query, and after some consistency checks and optimizations, the update primitives will be applied in the following order:
* '''Backups (1)''': {{Code|db:create-backup()}}
By default, it is not possible to mix different types of expressions in a query result. The outermost expression of a query must either be a collection of updating or non-updating expressions. But there are two ways out:
* The BaseX-specific <code>[[Database Update Module#dbupdate:output|dbupdate:output()]]</code> function bridges this gap: it caches the results of its arguments at runtime and returns them after all updates have been processed. The following example performs an update and returns a success message:
<pre class="brush:xquery">
</pre>
=Error Messages=
Along with the Update Facility, a number of new error codes and messages have been addedto the specification and BaseX. All errors are listed in the[[XQuery Errors#Update Errors|XQuery Errors]] overview. Please remember that the collected updates will be executed after the query evaluation. All logical errors will be raised before the updates are actually executed.
=Changelog=
;Version 9.0
* Updated: [[#Built-in Functions|Built-in Functions]]: serialization parameters
;Version 8.5
