Optional validations

Hello, great work with the library. I was wondering whether you are planning to add support for optional attributes (similar to @IsOptional() in class-validator).

[rhalff]

Hi, are you referring to https://github.com/typestack/class-validator written in typescript?

The description for @IsOptional() over there is:

Checks if given value is empty (=== null, === undefined) and if so, ignores all the validators on the property.

This seems to be different from what you're asking though (optional attributes) or do you mean the same thing?

This library currently doesn't have any conditional validators, I could have a look this week though as it seems doable.

Hello, this is exactly what I meant. I would like to provide validations for optional properties, which would be enforced only when the property is actually set.
Thank you for the feedback!

[timothychristensen]

@Andreas-Hubnao - we simply leverage the existing classes and create our own with the idea of NullOr...

Although I agree the @IsOptional() would be fantastic.

For example:

@immutable
@Constraint(validatedBy: NullOrSizeValidator)
@Target({ElementType.FIELD})
class NullOrSize extends ValidatorAnnotation {
  final int min;
  final int max;
  const NullOrSize({
    this.min,
    this.max,
    String message,
    List<String> groups,
  }) : super(message, groups);
}

class NullOrSizeValidator extends ConstraintValidator {
  final int max;
  final int min;

  NullOrSizeValidator({
    @required this.min,
    @required this.max,
  })  : assert(min != null),
        assert(max != null),
        super([min, max]);

  @override
  bool isValid(dynamic value, ValueContext context) {
    if (value == null) {
      return true;
    }

    if (value is String || value is Iterable || value is Map) {
      return min <= (value.length as int) && (value.length as int) <= max;
    }

    if (value is num) {
      return min <= value && value <= max;
    }

    return false;
  }

  @override
  Function message = (int min, int max, Object validatedValue) => '$validatedValue is not between $min and $max';
}

You'll only need to make sure you import BOTH the validator and the annotation, for example:

import 'package:yourpackage/src/validation/null_or_size.dart';
import 'package:yourpackage/src/validation/null_or_size_validator.dart';

We find this to be common for APIs requiring specific sizes of string values - or - they can be null.