XQuery Recipes

This page contains code snippets that mainly originate from our basex-talk mailing list.

Computed Elements

Returns dynamically named elements:

let $root := "element"
let $value := "hi"
let $contents := <foo>Bar!</foo>
return element { $root } {
  attribute { "about" } { $value }, $contents
}

The result is an XML fragment with <element> as root node:

<element about="hi">
  <foo>Bar!</foo>
</element>

Transform List to Tree

This snippet transform a flat list of elements with parentId-references to a nested list.

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')

results in

<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>

IP-Converter

This snippet converts an IP address to its numeric representation:

let $ip := '134.34.226.65'
return fold-left(
 function($n, $d) { 256 * $n + $d },
 0,
 map(xs:integer#1, tokenize($ip, '\.'))
)

results in

2250433089

Count number of files

This snippets returns the number of JPG files in a directory and its sub-directories:

basex "count(file:list('.',true(),'*.jpg'))"

The Linux equivalent is

find . | grep \.jpg$ | wc -l