AsyncRule class abstract

Contract for asynchronous validation rules.

Some rules cannot decide locally whether a value is valid. Uniqueness checks, remote existence lookups, or captcha verification all need an await before they can answer. AsyncRule extends Rule with a passesAsync method; the synchronous passes is a permissive placeholder that keeps sync-only validation flows working.

Validators that understand async rules should detect this subtype and await passesAsync instead of relying on passes. See Validator.validateAsync.

class Exists extends AsyncRule {
  Exists(this.endpoint);
  final String endpoint;

  @override
  Future<bool> passesAsync(String attr, dynamic value, Map<String, dynamic> data) async {
    final response = await Http.get(endpoint, query: {attr: value?.toString() ?? ''});
    return response.successful;
  }

  @override
  String message() => 'validation.exists';
}