Database Reference
In-Depth Information
update
insert
<LogEntry>
Something happened...
</LogEntry>
into
doc
(
'/db/logs/mainlog.xml'
)/
*
The following (somewhat more complicated) example makes sure that the number of
messages does not exceed 10, and that the most recent message is on top:
let
$
document
:=
doc
(
'/db/logs/mainlog.xml'
)
let
$
newentry
:=
<LogEntry>
Something happened...
</LogEntry>
return
update
delete
$
document
/
*
/
LogEntry
[
position
()
ge
10
],
if
(
exists
(
$
document
/
*
/
LogEntry
[
1
]))
then
update
insert
$
newentry
preceding
$
document
/
*
/
LogEntry
[
1
]
else
update
insert
$
newentry
into
$
document
/
*
All eXist XQuery update statements start with the keyword
update
, followed by an
update action. Available actions are
delete
,
insert
,
rename
,
replace
, and
value
.
The return type of an update statement is always the empty sequence
()
.
An eXist update statement can only be used to update persistent XML documents
stored in the database. It cannot be used to update temporary documents or docu‐
ment fragments stored in memory. For example, the following code fragment is ille‐
gal and will result in an error:
(: This is invalid: :)
let
$
document
as
document-node
()
:=
<Root><a/></Root>
return
update
insert
<b/>
into
$
document
/
*
You can use eXist's update statements anywhere in your XQuery main code or func‐
tion bodies. However, take care when using them inside a FLWOR expression return
statement. Update statements take effect immediately, and changing the structure
your query is looping over may lead to some unexpected results!
update delete
update delete
simply deletes nodes. Its syntax is:
update
delete
expr1
where
expr1
is an XQuery expression resolving to any kind of node. All nodes in
expr1
will be deleted by this statement.
Note that you cannot delete document root elements with
update delete
.
update insert
update insert
inserts content into an element node. Its syntax is:
update insert expr1 [ into | following | preceding ] expr2
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