Changes

The [https://en.wikipedia.org/wiki/%3F: ternary if] operator provides a short syntax for conditions. It is also called '''conditional operator''' or '''ternary operator'''. In most languages, the syntax is <code>a ? b : c</code>. As <code>?</code> and <code>:</code> have already been taken in XQuery, the syntax of Perl 6 is used:

(: if/then/else :)

if ($ok) then 1 else 0,

In XQuery 3.1, both branches of the <code>if</code> expression need to be specified. In many cases, only one branch is required, so the <code>else</code> branch was made optional in BaseX. If the second branch is omitted, an empty sequence will be returned if the effective boolean value of the test expression is false. Some examples:

if (doc-available($doc)) then doc($doc),

if (file:exists($file)) then file:delete($file),

If conditions are nested, a trailing else branch will be associated with the innermost <code>if</code>:

if ($a) then if($b) then '$a and $b is true' else 'only $a is true'

</syntaxhighlight>

In general, if you have multiple or nested if expressions, additional parentheses can improve the readibility of your code:

if ($a) then (

if($b) then '$a and $b is true' else 'only $a is true'

'''Example:'''

(: yields "!Hi! !there!" :)

replace('Hi there', '\b', '!', 'j')

[[Options|Local database options]] can be set in the prolog of an XQuery main module. In the option declaration, options need to be bound to the [[Database Module]] namespace. All values will be reset after the evaluation of a query:

declare option db:catalog 'etc/w3-catalog.xml';

doc('doc.xml')

Many optimizations in BaseX will only be performed if an expression is ''deterministic'' (i. e., if it always yields the same output and does not have side effects). By flagging an expression as nondeterministic, optimizations and query rewritings can be suppressed:

sum( (# basex:nondeterministic #) {

1 to 100000000

In analogy with option declarations and function annotations, XQuery locks can also set via pragmas. See [[Transaction Management#Options|Transaction Management]] for details and examples.

(# basex:write-lock CONFIGLOCK #) {

file:write('config.xml', <config/>)

* [[Indexes|Index access rewritings]] can be enforced. This is helpful if the name of a database is not static (see [[Indexes#Enforce Rewritings|Enforce Rewritings]] for more details):

(# db:enforceindex #) {

for $db in ('persons1', 'persons2', 'persons3')

* Node copying in node constructors can be disabled (see {{Option|COPYNODE}} for more details). The following query will consume much less memory than without pragma as the database nodes will not be fully duplicated, but only attached to the {{Code|xml}} parent element:

file:write(

'wrapped-db-nodes.xml',

'''Query:'''

declare function local:square($a) { $a * $a };

for $i in 1 to 3

'''Query after function inlining:'''

for $i in 1 to 3

return

'''Query after further optimizations:'''

for $i in 1 to 3

return $i * $i

'''Example:'''

(: disable function inlining; the full stack trace will be shown... :)

declare %basex:inline(0) function local:e() { error() };

'''Example:'''

declare %basex:lazy variable $january := doc('does-not-exist.xml');

if(month-from-date(current-date()) = 1) then $january else ()

In XQuery, some namespaces are statically bound to prefixes. The following query requires no additional namespaces declarations in the query prolog:

<xml:abc xmlns:prefix='uri' local:fn='x'/>,

fn:exists(1)

* Main modules have an expression as query body. Here is a minimum example:

'Hello World!'

</syntaxhighlight>

* Library modules start with a module namespace declaration and have no query body:

module namespace hello = 'http://basex.org/examples/hello';