Creating a ValueObject

Steps to create a ValueObject

Declare your class this way :

/// SingleValueObject
class Age extends SingleValueObject<InvalidAge, ValidAge> with _$Age {}

/// MultiValueObject
class GeoPoint extends MultiValueObject<InvalidGeoPoint, ValidGeoPoint>
    with _$GeoPoint {}

Add the imports and part statements, the @Modddel annotation, and the private empty constructor.

Add the factory constructor :

/// SingleValueObject
//...
factory Age(int value) //...

/// MultiValueObject
//...
factory GeoPoint({
  required int latitude,
  required int longitude,
}) //...

Create your failure(s) sealed class(es).

You can now run the generator, and then override and implement the "validate" methods.

Default validationSteps names

The name parameter of the ValidationStep is optional. If you omit it, it will be replaced by a default name :

Step	Default name	Example
1	Value1	InvalidAgeValue1
2	Value2	InvalidAgeValue2
3	Value3	InvalidAgeValue3
...	...	...

If there's only one step, then its default name is 'Value' (instead of 'Value1').

Complete Example

// ... Imports & Part statements

@Modddel(
  validationSteps: [
    ValidationStep([
      Validation('location', FailureType<GeoPointLocationFailure>()),
    ]),
  ],
)
class GeoPoint extends MultiValueObject<InvalidGeoPoint, ValidGeoPoint> with _$GeoPoint {
  GeoPoint._();

  factory GeoPoint({
      required int latitude,
      required int longitude,
  }) {
    return _$GeoPoint._create(
      latitude: latitude,
      longitude: longitude,
    );
  }

  @override
  Option<GeoPointLocationFailure> validateLocation(geoPoint) {
    if (geoPoint.latitude == 0 && geoPoint.longitude == 0) {
      return some(const GeoPointLocationFailure.nullIsland());
    }
    return none();
  }
}

@freezed
class GeoPointLocationFailure extends ValueFailure with _$GeoPointLocationFailure{
  /// Null Island is the point on the Earth's surface at zero degrees 
  /// latitude and zero degrees longitude (0°N 0°E)
  const factory GeoPointLocationFailure.nullIsland() = _NullIsland;
}