Bureaucrats, editor, reviewer, Administrators
13,550
edits
Changes
Jump to navigation
Jump to search
A [[Options|local database option]] can also be assigned locally via a pragma. Examples:==BaseX Pragmas==
* Whitespace chopping Many optimizations in BaseX will only be performed if an expression is disabled for a particular document ''deterministic'' (see {{Option|CHOP}}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:
* {{VersionThis pragma can be helpful when debugging your code. ==Database Pragmas== All [[Options|9local database options]] can be assigned via pragmas.0}}Some examples: * Enforce query to be rewritten for index rewriting access. This can e. g. be helpful if the name of a database name is not static (see [[Indexes#Enforce Rewritings|Enforce Rewritings]] for more examples):
file:base-dir() || 'wrapped-db-nodes.xml',
</pre>
Many optimizations and query rewritings can be disabled by marking an expression as non-deterministic:
<pre class="brush:xquery">
count( (# basex:non-deterministic #) { 1 to 10 })
→Regular expressions
=Pragmas=
<pre class="brush:xquery">
sum( (# dbbasex:chop false non-deterministic #) { doc('doc.xml' 1 to 100000000}) }
</pre>
<pre class="brush:xquery">
</pre>
* {{Version|9.0}}: Temporarily disable node copying in node constructors (see {{Option|COPYNODE}} for more details). The following query will be evaluated faster, and take much less memory, than without pragma, because the database nodes will not be fully copied, but only attached to the new {{Code|xml}} parent element:
<pre class="brush:xquery">
file:write(
(# db:copynode false #) {
<xml>{ db:open('huge') }</xml>
}
)
</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.
