XQuery/Dynamic Module Loading

Motivation You want to conditionally import a module. For example the module might provide a list of all the functions to style a web page such as header/footer and breadcrumbs. Method Module import We will use the XQuery function util:import-module(). This function has three arguments: $namespace: The full URI of the module that you are loading such as http://example.com/my-module $prefix: the prefix you want to use to reference each function in the module such as style $location: the database path that you will be loading the module from such as an absolute path/db/modules/my-module.xqm or a relative path my-module.xqm For example the following will import a module called my-module from the /db/modules collection.: util:import-module(xs:anyURI('http://example.com/my-module'), 'style', xs:anyURI('/db/modules/my-module.xqm')) The function xs:anyURI is used to cast each string into the URL type. Function invocation Because the namespace is declare dynamically, the imported functions have to be invoked using util:eval. The input to this function is a string containing an XQuery expression. e.g. util:eval('style:header()') Example The following will randomly load one of two style modules. xquery version "1.0"; declare option exist:serialize "method=xhtml media-type=text/html omit-xml-declaration=yes indent=yes"; let $module := if (math:random() < 0.5) then util:import-module( xs:anyURI('http://example.com/style-a'), 'style', xs:anyURI('style-a.xqm') ) else util:import-module( xs:anyURI('http://example.com/style-b'), 'style', xs:anyURI('style-b.xqm') ) return <html> <head> <title>Test of Dynamic Module Import</title> {util:eval('style:import-css()')} </head> <body> {util:eval('style:header()')} {util:eval('style:breadcrumb()')} <h1>Test of Dynamic Module Import</h1> {util:eval('style:footer()')} </body> </html> Run Style A Module Here is an example of a style module. It has four functions. One to import the CSS files, one for the header, one for the navigation breadcrumb and one for the footer. xquery version "1.0"; module namespace style='http://example.com/style-a'; declare function style:import-css() { <link type="text/css" rel="stylesheet" href="style-a.css"/> }; declare function style:header() { <div class="header"> <h1>Header for Style A</h1> </div> }; declare function style:breadcrumb() { <div class="breadcrumb"> <h1>Breadcrumb for Style A</h1> </div> }; declare function style:footer() { <div class="footer"> <h1>Footer for Style A</h1> </div> }; Style A CSS body { color: blue; } Style B Module xquery version "1.0"; module namespace style='http://example.com/style-b'; declare function style:import-css() { <link type="text/css" rel="stylesheet" href="style-b.css"/> }; declare function style:header() { <div class="header"> <h1>Header for Style B</h1> </div> }; declare function style:breadcrumb() { <div class="breadcrumb"> <h1>Breadcrumb for Style B</h1> </div> }; declare function style:footer() { <div class="footer"> <h1>Footer for Style B</h1> </div> }; Style B CSS body { color: red; }