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[[Category:XQuery]]<syntaxhighlight lang="xml">find . | grep \.jpg$ | wc -l</syntaxhighlight>
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This page contains code snippets that mainly originate from our [https://mailman.uni-konstanz.de/mailman/listinfo/basex-talk basex-talk] mailing list.
== Compact Notations ==
<code>if</code>/<code>not</code>/<code>else</code> constructs can look pretty verbose in XQuery.
However, some alternatives exist in order to make conditional code more compact:
* The [[XQuery 3.0#Simple Map Operator|Simple Map Operator]] can be used to trigger an action if a value has a single item. The following two expressions are equivalent:
<syntaxhighlight lang="xquery">
let $s := "X" return (
(: OLD :) if(count($s) = 1) then 'OK' else (),
(: NEW :) $s ! 'OK'
)
</syntaxhighlight>
In some cases, also the first solution can be written more compact. If we know that our input will always have 0-1 items, we can write <code>if(exists($s))</code>. If our input will never be an empty string, a zero, etc, it’s sufficient to write <code>if($s)</code>.
* If you want to choose the first non-empty item from two arguments, we can use the position predicate:
<syntaxhighlight lang="xquery">
let $s := "X" return (
(: OLD :) if(exists($s)) then $s else 'default',
(: NEW :) ($s, 'default')[1]
)
</syntaxhighlight>
Note that this only works if both of your inputs have zero or one items.
== Computed Elements ==
Returns dynamically named elements:
<pre classsyntaxhighlight lang="brush:xquery">let $nameroot := "element"let $class value := "hi"
let $contents := <foo>Bar!</foo>
return element { $name root } { attribute { "about" } { $class value }, $contents
}
</presyntaxhighlight>
The result is an XML fragment with <code><element></code> as root node:
<pre classsyntaxhighlight lang="brush:xml">
<element about="hi">
<foo>Bar!</foo>
</element>
</presyntaxhighlight> == Transform List to Tree ==This snippet transform a ''flat'' list of elements with <code>parentId</code>-references to a nested list. <syntaxhighlight lang="xquery">declare function local:link($entries as node()*, $id as xs:string) { let $entry := $entries[@id eq $id], $children := $entries[@parentId eq $id] return element entry { $entry/@*, for $child in $children return local:link($entries, $child/@id) }}; let $entries := <entries> <entry id="entry1" /> <entry id="entry2" parentId="entry1" /> <entry id="entry3" parentId="entry1" /> <entry id="entry4" parentId="entry2" /> <entry id="entry5" parentId="entry2" /> <entry id="entry6" parentId="entry3" /> <entry id="entry7" parentId="entry3" /> </entries>return local:link($entries/entry, 'entry1')</syntaxhighlight>results in<syntaxhighlight lang="xml"><entry id="entry1"> <entry id="entry2" parentId="entry1"> <entry id="entry4" parentId="entry2"/> <entry id="entry5" parentId="entry2"/> </entry> <entry id="entry3" parentId="entry1"> <entry id="entry6" parentId="entry3"/> <entry id="entry7" parentId="entry3"/> </entry></entry></syntaxhighlight> == IP-Converter == This snippet converts an IP address to its numeric representation: <syntaxhighlight lang="xquery">let $ip := '134.34.226.65'return fold-left( tokenize($ip, '\.')!xs:integer(.), 0, function($n, $d) { 256 * $n + $d })</syntaxhighlight>results in<syntaxhighlight lang="xml">2250433089</syntaxhighlight> == Count number of files == This snippets returns the number of JPG files in a directory and its sub-directories: <syntaxhighlight lang="xquery">basex "count(file:list('.',true(),'*.jpg'))"</syntaxhighlight> The Linux equivalent is
