Changes

It summarizes the update features of BaseX.

=Features=

===insert===

insert node (attribute { 'a' } { 5 }, 'text', <e/>) into /n

Insert enables you to insert a sequence of nodes into a single target node. Several modifiers are available to specify the exact insert location: insert into '''as first'''/'''as last''', insert '''before'''/'''after''' and insert '''into'''.

===delete===

delete node //n

The example query deletes all <code><n></code> elements in your database. Note that, in contrast to other updating expressions, the delete expression allows multiple nodes as a target.

===replace===

replace node /n with <a/>

The target element is replaced by the DOM node <code><a/></code>. You can also replace the value of a node or its descendants by using the modifier '''value of'''.

replace value of node /n with 'newValue'

All descendants of /n are deleted and the given text is inserted as the only child. Note that the result of the insert sequence is either a single text node or an empty sequence. If the insert sequence is empty, all descendants of the target are deleted. Consequently, replacing the value of a node leaves the target with either a single text node or no descendants at all.

===rename===

for $n in //originalNode

return rename node $n as 'renamedNode'

All <code>originalNode</code> elements are renamed. An iterative approach helps to modify multiple nodes within a single statement. Nodes on the descendant- or attribute-axis of the target are not affected. This has to be done explicitly as well.

===copy/modify/return===

copy $c := doc('example.xml')//originalNode[@id = 1]

modify rename node $c as 'copyOfNode'

return $c

The <code>originalNode</code> element with <code>@id=1</code> is copied and subsequently assigned a new QName using the rename expression. Note that the transform expression is the only expression which returns an actual XDM instance as a result. You can therefore use it to modify results and especially DOM nodes. This is an issue beginners are often confronted with. More on this topic can be found in the [[Update#Returning Results|XQUF Concepts]] section.

Query:

copy $c :=

<entry>

)

return $c

Result:

<entry>

<title>Copy of: Transform expression example</title>

<author>Joey</author>

</entry>

The <code><entry></code> element (here it is passed to the expression as a DOM node) can also be replaced by a database node, e.g.:

copy $c := (db:open('example')//entry)[1]

...

In this case, the original database node remains untouched as well, as all updates are performed on the node copy.

and all:

copy $c := doc("zaokeng.kml")

modify (

)

return $c

===update===

expression is bound as context item, and the second expression performs updates on this item.

<root/> update {

insert node <child/> into .

insert node "text" into child

}

===transform with===

The {{Code|transform with}} 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:

<xml>text</xml> transform with {

replace value of node . with 'new-text'

}

==Functions==

===Built-in Functions===

===User-Defined Functions===

If an updating function item is called, the function call must be prefixed with the keyword {{Code|updating}}. This ensures that the query compiler can statically detect if an invoked function item will perform updates or not:

let $node := <node>TO-BE-DELETED</node>

let $delete-text := %updating function($node) {

updating $delete-text(.)

)

As shown in the example, user-defined and anonymous functions can additionally be annotated as {{Code|%updating}}.

==Pending Update List==

* '''Backups (1)''': {{Code|db:create-backup()}}

The query…

insert node <b/> into /doc,

for $n in /doc/child::node()

return rename node $n as 'justRenamed'

…applied on the document…

<doc> <a/> </doc>

…results in the following document:

<doc> <justRenamed/><b/> </doc>

Despite explicitly renaming all child nodes of {{Code|<doc/>}}, the former {{Code|<a/>}} element is the only one to be renamed. The {{Code|<b/>}} element is inserted within the same snapshot and is therefore not yet visible to the user.

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:

If you want to modify nodes in main memory, you can use the [[Update#transform|transform expression]].

In BaseX, all updates are performed on database nodes or in main memory. By default, update operations do not affect the original input file (the info string "Updates are not written back" appears in the query info to indicate this). The following solutions exist to write XML documents and binary resources to disk:

* Functions like <code>[[#fn:put|fn:put]]</code> or <code>[[File Module#file:write|file:write]]</code> can be used to write single XML documents to disk. With <code>[[File Module#file:write-binary|file:write-binary]]</code>, you can write binary resources.

* The [[Commands#EXPORT|EXPORT]] command can be used write all resources of a databases to disk.

==Indexes==

More details are found in the article on [[Index#Updates|Indexing]].

=Error Messages=

=Changelog=

;Version 8.5