dartson

Dartson 1.0.0 is currently in alpha. The public API might be subject to change. For further details of potential breaks and a roadmap take a look at project 1.0.0.

Dartson is a dart library which converts Dart Objects into their JSON representation. It helps you keep your code clean of fromJSON and toJSON functions by providing a builder which generates the serialization methods.

Usage

Add the following lines to your pubspec.yaml in order to use dartson:

dependencies:
  dartson: ^1.0.0-alpha+4
  
dev_dependencies:
  build_runner: ^0.10.0

Dartson is using a central serializer instead of serializers for each object, therefore create a central file which refers the objects that need to be serialized:

import 'package:dartson/dartson.dart';
import 'package:some_dependency/some_class.dart';

import 'my_class.dart';

@Serializer(
  entities: [
    MyClass,
    SomeClass,
  ],
)
final Dartson<Map<String, dynamic>> serializer = _serializer$dartson;

Dartson encodes and decodes into a serializable Map (Map<String, dynamic>) by default. In order to encode and decode into a json string (in previous versions done by using Dartson.JSON) directly, call the useCodec method on the generated Dartson instance, which creates a new instance using the provided codec.

import 'dart:convert';

import 'package:dartson/dartson.dart';
import 'package:some_dependency/some_class.dart';

import 'my_class.dart';

@Serializer(
  entities: [
    MyClass,
    SomeClass,
  ],
)
final Dartson<String> serializer = _serializer$dartson.useCodec(json);

Private properties

It's not possible to encode / decode private properties. To set private properties, expose these within the constructor and provide a getter for encoding the entity.

Encoding / decoding lists

As of dartson >1.0.0 there are specific encodeList and decodeList methods. Because of type restrictions encodeList returns an Object and decodeList expects an Object. This should not cause any further actions when using json codec, however when working with the default serializer without any Codec, than a cast to List<Map<String, dynamic>> might be necessary when using the encodeList result.

main() {
  final result = serializer.encodeList([
	MyClass()..name = 'test1',
	MyClass()..name = 'test2',
  ]) as List<Map<String, dynamic>>;

  expect(result, allOf(isList, hasLength(2)));
  expect(result[0]['name'], 'test1');
  expect(result[1]['name'], 'test2');
}

Replacing entities

Sometimes entities are automatically generated and as such cannot contain any handwritten code, which could provide further logic and reduce complexity. This is where the replacement feature of dartson can help.

Here an example of an entity called Money which is replaced using MoneyImpl for replacing the operators.

import 'package:dartson/dartson.dart';
import 'package:dartson/transformers/date_time.dart';

// Imagine Money and Product couldn't be touched.
class Money {
  double net;
  double gross;
}

class Product {
  Money price;
  String name;
}


class MoneyImpl extends Money {
  operator +(dynamic ob) {
    if (obj is! Money) {
      throw TypeError();
    }
    
    net += ob.net;
    gross += ob.gross;
  }
}


@Serializer(
  entities: [
    Money,
    Product,
  ],
  replacements: {
    Money: MoneyImpl,
  },
  transformers: [
    DateTimeParser,
  ],
)
final Dartson serializer = _serializer$dartson;

Extending the serializer

Dartson supports extending serializers to provide a module approach. This is necessary to support functionality like deferred loading. This also may improve build times, so when changing an entity only a part of the serializer is regenerated.

serializer_init.dart

import 'dart:convert';

import 'package:dartson/dartson.dart';
import 'package:some_dependency/some_class.dart';

import 'my_class.dart';

@Serializer(
  entities: [
    MyClass,
    SomeClass,
  ],
)
final Dartson<String> serializer = _serializer$dartson.useCodec(json);

serializer_second.dart

import 'package:dartson/dartson.dart';

import 'other_class.dart';
import 'serializer_init.dart' as fs;

@Serializer(
  entities: [
    OtherClass,
  ],
)
final Dartson<String> serializer = fs.serializer.extend(_serializer$dartson);

Notice that extend provides a completely new instance of Dartson. Also the entities provided by the serializer on which extend was called can be overwritten by the entities used in the serializer passed as the argument (in this case: _serializer$dartson entities may overwrite fs.serializer entities).

Writting custom TypeTransformers

Transformers are used to encode / decode none serializable types that shouldn't be treated as objects / lists (for example DateTime).

/// A simple DateTime transformer which uses the toString() method.
class DateTimeParser implements TypeTransformer<String, DateTime> {
  // Make sure to add a constant constructor, because dartson will initiate all tranformers
  // as constant to improve dart2js compilation.
  const DateTimeParser();
  DateTime decode(String value) => DateTime.parse(value);
  String encode(DateTime value) => value.toString();
}

In order to use the TypeTransformer you need to register the transformer for the serializer:

import 'package:dartson/dartson.dart';
import 'package:dartson/transformers/date_time.dart';

import 'my_class.dart';

@Serializer(
  entities: [
    MyClass,
  ],
  transformers: [
    DateTimeParser,
  ],
)
final Dartson serializer = _serializer$dartson;

Roadmap for 1.0.0 alpha/beta

• First alpha release evaluates and tests the reuse of json_serializable (refactorings during the alpha/beta will be necessary)
• Additional functionality from proposals will be ported
• Looking for feedback in regards of usability from users
• Further benchmarking of potential bottlenecks because of single point of
  the builder

Further features planned

• See doc/proposal for general features
• Add tool to generate serializer.dart based on serializer.decode<T>() and serializer.encode(T) usage
• Add analyzer plugin to detect potential issues of used entities which are not present in the serializer definition