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Input System - Default Sources

When to Use

Use default sources to provide fallback values when inputs aren't explicitly collected from users.

Default sources provide fallback values when inputs aren't explicitly collected. Three source types: literal values, config references, environment variables.

Items: The Three Default Sources

source: value

Description: Literal default value Parameters: | Param | Type | Notes | |-------|------|-------| | value | primitive | Literal string, int, bool, or float |

Usage Example: 

input:
  site_name:
    data_type: string
    default:
      source: value
      value: 'Default Site Name'
Gotchas: No fallback; value is the default

source: config

Description: Read default from active config Parameters: | Param | Type | Notes | |-------|------|-------| | config | array | [config_name, property_path] | | fallback | primitive | Optional; used if config doesn't exist |

Usage Example: 

input:
  site_mail:
    data_type: string
    default:
      source: config
      config: [system.site, mail]
      fallback: 'admin@example.com'
Gotchas: Config must exist unless fallback provided; throws exception if config missing and no fallback

source: env

Description: Read default from environment variable Parameters: | Param | Type | Notes | |-------|------|-------| | env | string | Environment variable name | | fallback | primitive | Optional; used if env var not set |

Usage Example: 

input:
  api_key:
    data_type: string
    default:
      source: env
      env: DRUPAL_API_KEY
      fallback: ''
Gotchas: Environment variables are always strings; no type coercion; missing var without fallback throws exception

Common Mistakes

  • Using config source without fallback on new installs → Config likely doesn't exist yet; provide fallback
  • Forgetting environment variables are strings → ENABLE_FEATURE=1 is string "1", not boolean true
  • Not validating fallback matches data type → Fallback should be same type as data_type (though cast happens)
  • Using deeply nested config paths → Only supports config.get('key'), not config.get('nested.key.path'); use dot syntax in key
  • Assuming config source works for all config → Only works for simple config, not config entity properties

See Also