XQuery Update Extension
This article describes eXist-db's extension to XQuery for updating nodes in the database.
This extension was created well before the W3C working group created the XQuery Update Facility 1.0 recommendation and therefore differs substantially from it.
The XQuery update extension was designed for updating persistent documents stored in the database. It does not work for updating temporary document fragments constructed within an query.
let $node := <root><a/></root> return update insert <b/> into $node/a
$node is an in-memory constructed element (rather than a node stored
in the database) the query has no effect and simply returns the empty element.
All update statements start with the keyword
update, followed by an update
Available actions are:
rename. The return type of an update expression is
An update statement may occur at any position within the XQuery main code or a function body.
update within the return clause of a FLWOR expression, be
cautious when deleting or replacing nodes that are still being used by the enclosing code.
This is because a delete or replace will be processed immediately, and so the deleted or
replaced node will no longer be available to the query. Such actions can corrupt
For example, the following expression will throw the database into an inconsistent state
//address returns more than one node:
for $address in //address return update delete //address
However, an expression like the following is safe as it only modifies the current
iteration variable. The following example only deletes
$address (the current
iteration variable) instead of
//address (all addresses in the
for $address in //address return update delete $address
update insert expr ( into | following | preceding ) exprSingle
Inserts the content sequence specified in
expr into the element node passed
expr must evaluate to
a node set. If
exprSingle contains more than one element node, the modification
will be applied to each of the nodes. The position of the insertion is determined by the
The content is appended after the last child node of the specified elements.
The content is inserted immediately after the node specified in
The content is inserted before the node specified in
update replace expr with exprSingle
Replaces the nodes returned by
expr with the nodes in
expr must evaluate to a single element, attribute or
text node. If it is an element,
exprSingle must contain a single element node.
If it is an attribute or text node, the value of the attribute or the text node is set to
the concatenated string values of all nodes in
cannot be the root element of a document.
update value expr with exprSingle
Updates the content of all nodes in
expr with the items in
expr is an attribute or text node, its value will
be set to the concatenated string value of all items in
update delete expr
Removes all nodes in
expr from their document.
expr cannot be the root element of a
update rename expr as exprSingle
Renames the nodes in
expr using the string value of the first item in
exprSingle as the
new name of the node.
expr should evaluate to a set of elements or attributes.
be the root element of a document.