Nunjucks Helpers for Skeleton Entities

Skeleton Entities are rendered with Nunjucks using the ${{ ... }} syntax.

Standard Nunjucks syntax is available in skeleton rendering, including conditions, loops, and built-in filters. This page documents the Witboost-specific helpers available in Skeleton Entities, plus dump because it is the built-in filter used most often in Witboost skeletons.

info

The helpers documented here are available when Witboost renders:

• catalog-info.yaml
• parameters.yaml expressions in the parameters, values, readonly, and environmentParameters sections
• refs.<name>.config in parameters.yaml

The variables available in each phase differ. For example, refs are available only when rendering catalog-info.yaml, while refs.<name>.config can use parameters, values, and readonly.

dump

dump is a built-in Nunjucks filter commonly used in Skeleton Entities to serialize a value while preserving its type.

Use it when you want a string, object, array, boolean, number, or map to be emitted as valid YAML.

Input:

• any scalar value, array, or object

Output:

• a serialized representation of that value, suitable for insertion into YAML

Example input:

parameters:
  owner: group:finance-data
  tags:
    - pii
    - finance

Example usage:

%SKELETON
kind: Component
spec:
  owner: ${{ parameters.owner | dump }}
  tags: ${{ parameters.tags | dump }}

Example output:

kind: Component
spec:
  owner: group:finance-data
  tags:
    - pii
    - finance

parseEntityRef

parseEntityRef is a filter that parses an entity reference into its structured parts.

Use it when you need to extract the kind, namespace, or name from a Witboost entity reference.

Input:

• a Witboost entity reference string

Output:

• an object with the parsed entity reference parts, including kind, namespace, and name

Example input:

group:default/finance-data

Example output:

kind: group
namespace: default
name: finance-data

Example usage:

%SKELETON
kind: Component
metadata:
  description: Owned by team ${{ (parameters.owner | parseEntityRef).name }}

pick

pick is a filter that extracts a nested field from an object using a dot-separated path.

Use it when an object contains nested data and you want a single field.

Input:

• first argument: an object or array
• second argument: a dot-separated path string such as spec.owner or @graph.0.@id

Output:

• the value found at that path
• null or undefined if the path does not resolve to a value in the input object

Example input:

spec:
  owner: group:finance-data
  mesh:
    maturity: strategic

Example output with pick('spec.owner'):

group:finance-data

Example usage:

%SKELETON
kind: Component
spec:
  mesh:
    maturity: ${{ parameters.metadata | pick('mesh.maturity') }}

parseRdf(...)

parseRdf is a global helper that parses RDF content and returns an object value that can be used in Nunjucks and that follows JSON-LD syntax.

Use it when the skeleton needs to inspect RDF data available in the rendering context.

Input:

• the RDF content as a string
• an optional format string

Supported format strings:

• auto
• turtle
• n3
• trig
• ntriples
• nquads
• rdfxml
• jsonld

If the format is omitted, the parser tries to auto-detect it from the input content and the optional parsing metadata.

Output:

• null if the input content is null, undefined, or an empty string
• otherwise, an object using JSON-LD syntax, typically containing @context and @graph

Example input in Turtle format:

@prefix ex: <http://example.com/> .
ex:Tom a ex:Person ;
  ex:name "Tom" .

Example output for Turtle input:

'@context':
  ex: http://example.com/
'@graph':
  - '@id': ex:Tom
    '@type': ex:Person
    ex:name: Tom

Example input in RDF/XML format:

<?xml version="1.0"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:ex="http://example.com/">
  <rdf:Description rdf:about="http://example.com/Tom">
    <rdf:type rdf:resource="http://example.com/Person" />
    <ex:name>Tom</ex:name>
  </rdf:Description>
</rdf:RDF>

Example output for RDF/XML input:

'@context':
  ex: http://example.com/
  rdf: http://www.w3.org/1999/02/22-rdf-syntax-ns#
'@graph':
  - '@id': ex:Tom
    '@type': ex:Person
    ex:name: Tom

Example input already written with JSON-LD syntax:

{
  "@context": {
    "ex": "http://example.com/"
  },
  "@id": "ex:Tom",
  "@type": "ex:Person",
  "ex:name": "Tom"
}

Example output for JSON-LD input:

'@context':
  ex: http://example.com/
'@graph':
  - '@id': ex:Tom
    '@type': ex:Person
    ex:name: Tom

Example usage in a skeleton:

%SKELETON
kind: Component
metadata:
  annotations:
    ontology-subject: ${{ parseRdf(parameters.ontology, 'turtle') | pick('@graph.0.@id') }}

Rendered catalog-info.yaml:

metadata:
  annotations:
    ontology-subject: ex:Tom

Practical Notes

• Use dump whenever you inject arrays, maps, or nested objects into YAML.
• parseEntityRef and pick are filters, so they are used with the | syntax.
• parseRdf is a global helper, so it is called like a function.