How to set a default after the fact

[ronkorving]

I have a project where I put a lot of overridable values into convinct, and a common use-case I encounter is that I want to set default values late.

Example:

schema.yml:

organization:
  name:
    doc: Name of the organization
    format: String
    default: null
    arg: organization-name
domainName:
  doc: The domain name to be registered for the website
  format: String
  default: null
  arg: domain-name

I would like the domain name to default to ${organization.name}.awesomewebsites.com. The organization-name is not optional; it has to be provided. But the domain-name can be custom, but has a very obvious default based on the organization-name.

How can I achieve this with convict? Assuming this is currently impossible, I can see 3 theoretical solutions:

Via templates

schema.yml:

organization:
  name:
    doc: Name of the organization
    format: String
    default: null
    arg: organization-name
domainName:
  doc: The domain name to be registered for the website
  format: String
  default: '${organization.name}.awesomewebsites.com'   // convict will resolve this late, when the default is first needed
  arg: domain-name

Benefit:

• You could still print the default in --help output.

Via a default-function

schema.js:

module.exports = {
  organization: {
    name: {
      doc: 'Name of the organization',
      format: String,
      default: null,
      arg: 'organization-name'
    }
  },
  domainName: {
    doc: 'The domain name to be registered for the website',
    format: String,
    default: (config) => {
      return config.get('organization.name') + '.awesomewebsites.com';
    },
    arg: 'domain-name'
  }
};

Benefit:

• Most powerful solution wrt. the actual value (allowing conditional logic).
• Is in the spirit of the "Usage" example in the readme (using env/NODE_ENV).

Via API

const config = convict(mySchema);
config.loadFile('config.yml');
config.setDefault('domainName', config.get('organization.name') + '.awesomewebsites.com');

Drawback:

• Default value no longer exists in the same file as the schema.

Benefit:

• Allows schema to be JSON or YAML (but format and coerce already defy that anyway).

I would love to hear what y'all think about feasibility and if there's any preference wrt. the solutions. Thanks!

[A-312]

Similar to #237

Solution 4

Add compiler functions which allow custom functions, like that :

list = {};
convict.addCompiler('value', (v) => v.format(..., (k) => config.get(k)))
const config = convict(mySchema);
config.load({ config: '', configPath: '' })
config.compile()
config.validate()