Transformer

Transformer is a way to convert the input value to another type. This is useful when you want to convert the input value to another type before the validation process.

You can also use the transformer to handle the error when the conversion failed

Using Transformer

You can use the transformer parameter to provide a transformer to the supported schema.

import 'package:validasi/validasi.dart';

void main() {
    final schema = Validasi.number(transformer: NumberTransformer());

    final result = schema.tryParse('10');

    print(result.value); // 10
}

When the conversion failed, the transformer will return an error message (invalidType).

Built-in Transformers

Validasi provides a few built-in transformer:

• NumberTransformer
• StringTransformer
• DateTransformer

NumberTransformer

The NumberTransformer is used to convert the input value to a number. This transformer will convert the input value to a number using the num.parse method.

import 'package:validasi/validasi.dart';

final schema = Validasi.number(transformer: NumberTransformer()); 
print(schema.tryParse('10').value); // 10

StringTransformer

The StringTransformer is used to convert the input value to a string. This transformer will convert the input value to a string using the toString method.

import 'package:validasi/validasi.dart';

final schema = Validasi.string(transformer: StringTransformer()); 
print(schema.tryParse(10).value); // '10'

DateTransformer

The DateTransformer is used to convert the input value to a date. This transformer will convert the input value to a date using the DateFormat.tryParse method.

import 'package:validasi/validasi.dart';

final schema = Validasi.date(transformer: DateTransformer()); 
print(schema.tryParse('2021-01-01').value); // DateTime(2021-01-01 00:00:00.000)

Building your own Transformer

You can also build your own transformer by extending the Transformer class.

import 'package:validasi/validasi.dart';

class MyTransformer extends Transformer<String> {
    @override
    String? transform(value, fail) {
        return convert(value);
    }
}

The transform method will receive the input value and the fail function. You can use the fail function to handle the error when the conversion failed.

The fail function accept a message as the parameter. You can use this message as the error message when the conversion failed. When the conversion fail, the transformer will return an error message (invalidType).

The transformer could also return null. It could fails depend whatever nullable is set or not. If not, then the required rule will run and return the error message (required). See Execution Flow for more information.