Serve virtual resources

In addition to sh:targetNode and sh:targetClass, a specialised target can be used to match resources based on URL patterns. Such resources do not have to exist as triples in the database but can be generated on-the-fly by the server.

For example, if you have a collection resource, such as http://example.org/projects, and you would like to implement pagination using URL query parameters, you can define a patterned target to match requests to http://example.org/projects/1, http://example.org/projects/2, etc.

PREFIX code: <https://code.described.at/>
PREFIX sh: <http://www.w3.org/ns/shacl#>
PREFIX kl: <https://kopflos.described.at/>

[
  a kl:ResourceShape ;
  sh:target
    [
      a kl:PatternedTarget ;
      # Capture the page number in the URL
      kl:regex "/projects(/(?<page>\\d+))?" ;
    ] ;
  kl:handler
    [
      a kl:Handler ;
      kl:method "GET" ;
      code:implementedBy
        [
          a code:EcamScriptModule ;
          code:link <file:handler/projects.js#getCollection> ;
          # Pass the page number as an argument to the handler
          code:arguments ( "${page}"^^code:EcmaScriptTemplateLiteral ) ;
        ] ;
    ] ;
] .

tip

The pattern is matched against the path part of the URL only.

By taking advantage of named capture groups in the regular expression, you can extract parts of the URL. They can also be accessed programmatically from subjectVariables in a handler.

import { Handler } from '@kopflos-cms/core'

export function getCollection (page: string): Handler {
  return ({ subjectVariables }) => {
    // subjectVariables.page === page
  }
}

warning

Currently only regular expression patterns are supported. In a future release support for RFC6570 URI templates and express-style will be added.