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A ==BaseX Pragmas== 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 non-deterministic, optimizations and query rewritings can be suppressed: <pre class="brush:xquery">sum( (# basex:non-deterministic #) { 1 to 100000000})</pre> This pragma can be helpful when debugging your code. ==Database Pragmas== All [[Options|local database optionoptions]] can also be assigned locally via pragmas. Some examples: * Enforce query to be rewritten for index access. This can e. g. be helpful if the name of a pragmadatabase is not static (see [[Indexes#Enforce Rewritings|Enforce Rewritings]] for more examples):
Many optimizations * Temporarily disable node copying in node constructors (see {{Option|COPYNODE}} for more details). The following query will be evaluated faster, and query rewritings can take much less memory, than without pragma, because the database nodes will not be disabled by marking an expression as non-deterministicfully copied, but only attached to the new {{Code|xml}} parent element:
countfile:write( 'wrapped-db-nodes.xml', (# basexdb:non-deterministic copynode false #) { 1 to 10 <xml>{ db:open('huge') }</xml> })
→Regular expressions
=Pragmas=
<pre class="brush:xquery">
(# db:chop false enforceindex #) { doc for $db in ('doc.xmlpersons1', 'persons2', 'persons3') return db:open($db) //name[text() = 'John']}
</pre>
<pre class="brush:xquery">
</pre>
The annotation ensures that an error will only be thrown if the condition yields true. Without the annotation, the error will always be raised, because the referenced document is not found.
=Functions=
==Regular expressions==
{{Mark|Introduced with Version 9.1:}}
In analogy with Saxon, you can specify the flag {{Code|j}} to revert to Java’s default regex parser. For example, this allows you to use the word boundary option {{Code\b}}, which has not been included in the XQuery grammar for regular expressions:
'''Example:'''
<pre class="brush:xquery">
(: yields "!Hi! !there!" :)
fn:replace('Hi there', '\b', '!', 'j')
</pre>
=Serialization=
Various other extensions are described in the articles on [[Full-Text#BaseX Features|XQuery Full Text]] and [[Updates|XQuery Update]].
=Changelog=
# Version 9.1:
* Added: [[#Regular expressions]], {{Code|j}} flag for using Java’s default regex parser.
