DSON

Build Status

DSON is a dart library which converts Dart Objects into their JSON representation.

This library was initially a fork from Dartson. Now it contains some differences:

  • Dartson uses custom transformers to convert objects to JSON. This produce faster and smaller code after dart2Js. Instead DSON uses reflectable library and transformer. This should produce code as fast and small as Dartson transformer.
  • DSON has the ability to serialize cyclical objects by mean of depth parameter, which allows users to specify how deep in the object graph they want to serialize.
  • DSON has the ability to exclude attributes for serialziation in two ways.
  • Using @ignore over every attribute. This make excluding attributes too global and hardcoded, so users can only specify one exclusion schema.
  • Using exclude map as parameter for toJson method. This is more flexible, since it allows to have many exclusion schemas for serialization.
  • DSON uses the annotation @serializable instead @entity which is used by Dartson.

Configuration

1\. Add dependencies to pubspec.yaml

...
dependencies:
  ...
  dson: ^0.3.3
  reflectable: ^0.5.4           # this one is only needed for client/browser side apps
  ...
transformers:
- reflectable:                  # this transformer is also only needed for client/browser apps
    entry_points:
      - web/main.dart
...

To be able to use DSON on client side applications it is needed to add both: reflectable dependency and its transformer. If you don't add them you will not be able to run the app in the browser and the dart2js compiler will fail or throws some warnings about annotation @MirrorUsed.

Convert objects to JSON strings

To convert objects to JSON strings you only need to use the toJson function, annotate the object with @serializable and pass the object to the toJson function as parameter:

import 'package:dson/dson.dart';

@serializable
class Person {
  int id;
  String firstName;
  var lastName; //This is a dynamic attribute could be String, int, duble, num, date or another type
  double height;
  DateTime dateOfBirth;

  @SerializedName("renamed")
  String otherName;
  

  @ignore
  String notVisible;

  // private members are never serialized
  String _private = "name";

  String get doGetter => _private;
}

void main() {
  Person object = new Person()
    ..id = 1
    ..firstName = "Jhon"
    ..lastName = "Doe"
    ..height = 1.8
    ..dateOfBirth = new DateTime(1988, 4, 1, 6, 31)
    ..otherName = "Juan"
    ..notVisible = "hallo";

  String jsonString = toJson(object);
  print(jsonString);
  // will print: '{"id":1,"firstName":"Jhon","lastName":"Doe","height":1.8,"dateOfBirth":"1988-04-01T06:31:00.000","renamed":"Juan","doGetter":"name"}'
}

Converting objects to Maps

To convert objects to Maps you only need to use the toMap function, annotate the object with @serializable and pass the object to toMap function as parameter:

import 'package:dson/dson.dart';

@serializable
class Person {
  int id;
  String firstName;
  var lastName; //This is a dynamic attribute could be String, int, duble, num, date or another type
  double height;
  DateTime dateOfBirth;

  @SerializedName("renamed")
  String otherName;
  

  @ignore
  String notVisible;

  // private members are never serialized
  String _private = "name";

  String get doGetter => _private;
}

void main() {
  Person object = new Person()
    ..id = 1
    ..firstName = "Jhon"
    ..lastName = "Doe"
    ..height = 1.8
    ..dateOfBirth = new DateTime(1988, 4, 1, 6, 31)
    ..otherName = "Juan"
    ..notVisible = "hallo";

  Map map = toMap(object);
  print(map);
  // will print: '{id:1, firstName: Jhon, lastName: Doe, height: 1.8, dateOfBirth: 1988-04-01T06:31:00.000, renamed: Juan, doGetter: name}'
}

Serializing Cyclical Objects

To serialize objects that contains Cyclical References it would be needed to use the annotation @cyclical. If this annotation is present and the depth variable is not set then the non-primitive objects are not going to be parsed and only the id (or hashmap if the object does not contains id) is going to be present. Let's see next example:

import 'package:dson/dson.dart';

@serializable
@cyclical
class Employee {
  int id;
  String firstName;
  String lastName;
  
  Address address;
  
  Employee manager;
}

@serializable
@cyclical
class Address {
  int id;
  String street;
  String city;
  String country;
  String postalCode;
  
  Employee owner;
}


void main() {
  var manager = new Employee()
    ..id = 1
    ..firstName = 'Jhon'
    ..lastName = 'Doe';
  manager.address = new Address()
      ..id = 1
      ..street = 'some street'
      ..city = 'Miami'
      ..country = 'USA'
      ..owner = manager;

  var employee = new Employee()
    ..id = 2
    ..firstName = 'Luis'
    ..lastName = 'Vargas'
    ..manager = manager;
  employee.address = new Address()
    ..id = 2
    ..street = 'some street'
    ..city = 'Miami'
    ..country = 'USA'
    ..owner = employee;
    
  print(toJson(employee)); //will print: '{"id":2,"firstName":"Luis","lastName":"Vargas","address":{"id":2},"manager":{"id":1}}'
  
  print(toJson(employee.address)); // will print: '{"id":2,"street":"some street","city":"Miami","country":"USA","owner":{"id":2}}'
  
  // depth is a optional parameter that could be a list that should contains strings or Maps<String, Map>
  print(toJson(employee, depth: ['address']));
  /* will print:
           '{"id":2,"firstName":"Luis","lastName":"Vargas",'
              '"address":{"id":2,"street":"some street","city":"Miami","country":"USA","owner":{"id":2}},'
              '"manager":{"id":1}}'
  */
  
  print(toJson(employee, depth: [{'manager': ['address']}, 'address']));
  /* will print:
         '{"id":2,"firstName":"Luis","lastName":"Vargas",'
            '"address":{"id":2,"street":"some street","city":"Miami","country":"USA",'
              '"owner":{"id":2}},'
            '"manager":{"id":1,"firstName":"Jhon","lastName":"Doe",'
              '"address":{"id":1,"street":"some street","city":"Miami","country":"USA","owner":{"id":1}}}}');
  */
}

as you can see employee has an address, and the address has an owner of type Employee. If the property id is not present in the object then it is going to take the hashcode value from the object as reference. And finally, the depth parameter passed to serialize function tells serializer how deep you want to go throw the reference. This help us not only to avoid cyclical reference, but to determine what referenced objects should be serialized.

The same applies for lists:

import 'package:dson/dson.dart';

@serializable
@cyclical
class Student {
  int id;
  String name;
  
  List<Course> courses;
}

@serializable
@cyclical
class Course {
  int id;
  
  DateTime beginDate;
  
  List<Student> students;
}

void main() {
  
  var student1 = new Student()
      ..id = 1
      ..name = 'student1',
    student2 = new Student()
      ..id = 2
      ..name = 'student2',
    student3 = new Student()
      ..id = 3
      ..name = 'student3',
    course1 = new Course()
      ..id = 1
      ..beginDate = new DateTime.utc(2015, 1, 1)
      ..students = [student1, student2],
    course2 = new Course()
      ..id = 2
      ..beginDate = new DateTime.utc(2015, 1, 2)
      ..students = [student2, student3],
    course3 = new Course()
      ..id = 3
      ..beginDate = new DateTime.utc(2015, 1, 3)
      ..students = [student1, student3];
  
  student1.courses = [course1, course3];
  student2.courses = [course1, course2];
  student3.courses = [course2, course3];
  
  var students = [student1, student2, student3]; 
  
  print(toJson(student1)); // will print: '{"id":1,"name":"student1","courses":[{"id":1},{"id":3}]}'

  print(toJson(student1, depth: ['courses']));
  /* will print:
      '{'
        '"id":1,'
        '"name":"student1",'
        '"courses":['
          '{"id":1,"beginDate":"2015-01-01T00:00:00.000Z","students":[{"id":1},{"id":2}]},'
          '{"id":3,"beginDate":"2015-01-03T00:00:00.000Z","students":[{"id":1},{"id":3}]}'
        ']'
      '}');
   */

  print(toJson(student1.courses)); 
  /* will print:
      '['
        '{"id":1,"beginDate":"2015-01-01T00:00:00.000Z","students":[{"id":1},{"id":2}]},'
        '{"id":3,"beginDate":"2015-01-03T00:00:00.000Z","students":[{"id":1},{"id":3}]}'
      ']');
  */
  
  print(toJson(student2.courses, depth: ['students']));
  /* will print: 
      '['
        '{"id":1,"beginDate":"2015-01-01T00:00:00.000Z","students":['
          '{"id":1,"name":"student1","courses":[{"id":1},{"id":3}]},'
          '{"id":2,"name":"student2","courses":[{"id":1},{"id":2}]}'
        ']},'
        '{"id":2,"beginDate":"2015-01-02T00:00:00.000Z","students":['
          '{"id":2,"name":"student2","courses":[{"id":1},{"id":2}]},'
          '{"id":3,"name":"student3","courses":[{"id":2},{"id":3}]}'
        ']}'
      ']'
   */
}

Without the annotation @cyclical the program is going to throw a stack overflow error caused by the serializing of cyclical objects.

Excluding attributes from being serialized

To exclude parameter from being serialized we have two options the first option is using @ignore over the attribute to ignore. However this approach is too global. What I want to say with this is that the attribute is going to be ignored always.

Another way to exclude attributes is adding the parameter exclude to serialize function. In this way we only exclude those attributes during that serialization.

library example;

import 'package:dson/dson.dart';

@serializable
@cyclical
class Student {
  int id;
  String name;
  
  @DsonType(Course) // This annotation is only neede for client side applications
  List<Course> courses;
}

@serializable
@cyclical
class Course {
  int id;
  
  DateTime beginDate;
  
  @DsonType(Student) // This annotation is only neede for client side applications
  List<Student> students;
}

void main() {
  
  var student1 = new Student()
      ..id = 1
      ..name = 'student1',
    student2 = new Student()
      ..id = 2
      ..name = 'student2',
    student3 = new Student()
      ..id = 3
      ..name = 'student3',
    course1 = new Course()
      ..id = 1
      ..beginDate = new DateTime.utc(2015, 1, 1)
      ..students = [student1, student2],
    course2 = new Course()
      ..id = 2
      ..beginDate = new DateTime.utc(2015, 1, 2)
      ..students = [student2, student3],
    course3 = new Course()
      ..id = 3
      ..beginDate = new DateTime.utc(2015, 1, 3)
      ..students = [student1, student3];
  
  student1.courses = [course1, course3];
  student2.courses = [course1, course2];
  student3.courses = [course2, course3];
  
  var students = [student1, student2, student3]; 
  
  print(toJson(student1)); // will print: '{"id":1,"name":"student1","courses":[{"id":1},{"id":3}]}'

  print(toJson(student1, depth: 'courses', exclude: 'name'));
  /* will print:
      '{'
        '"id":1,'
        '"courses":['
          '{"id":1,"beginDate":"2015-01-01T00:00:00.000Z","students":[{"id":1},{"id":2}]},'
          '{"id":3,"beginDate":"2015-01-03T00:00:00.000Z","students":[{"id":1},{"id":3}]}'
        ']'
      '}');
   */

  print(toJson(student1.courses, exclude: 'beginDate')); 
  /* will print:
      '['
        '{"id":1,"students":[{"id":1},{"id":2}]},'
        '{"id":3,"students":[{"id":1},{"id":3}]}'
      ']');
  */
  
  print(toJson(student2.courses, depth: 'students', exclude: {'students': 'name'}));
  /* will print: 
      '['
        '{"id":1,"beginDate":"2015-01-01T00:00:00.000Z","students":['
          '{"id":1,"courses":[{"id":1},{"id":3}]},'
          '{"id":2,"courses":[{"id":1},{"id":2}]}'
        ']},'
        '{"id":2,"beginDate":"2015-01-02T00:00:00.000Z","students":['
          '{"id":2,"courses":[{"id":1},{"id":2}]},'
          '{"id":3,"courses":[{"id":2},{"id":3}]}'
        ']}'
      ']'
   */
   
   print(toJson(student2.courses, depth: 'students', exclude: ['beginDate', {'students': 'name'}]));
  /* will print: 
      '['
        '{"id":1,"students":['
          '{"id":1,"courses":[{"id":1},{"id":3}]},'
          '{"id":2,"courses":[{"id":1},{"id":2}]}'
        ']},'
        '{"id":2,"students":['
          '{"id":2,"name":"student2","courses":[{"id":1},{"id":2}]},'
          '{"id":3,"name":"student3","courses":[{"id":2},{"id":3}]}'
        ']}'
      ']'
   */
}

Convert JSON strings to objects

To convert JSON strings to objects you only need to use the fromJson and fromJsonList functions and pass the json string to deserialize and the Type of the object as parameters:

library example;

import 'package:dson/dson.dart';

@serializable
class EntityClass {
  String name;
  String _setted;
  
  @SerializedName("renamed")
  bool otherName;
  
  @ignore
  String notVisible;
  
  @DsonType(EntityClass) // This annotation is only neede for client side applications
  List<EntityClass> children;
  
  set setted(String s) => _setted = s;
  String get setted => _setted;
}

void main() {
  EntityClass object = fromJson('{"name":"test","renamed":true,"notVisible":"it is", "setted": "awesome"}', EntityClass);
  
  print(object.name); // > test
  print(object.otherName); // > blub
  print(object.notVisible); // > it is
  print(object.setted); // > awesome
  
  // to deserialize a list of items use [fromJsonList]
  List<EntityClass> list = fromJsonList('[{"name":"test", "children": [{"name":"child1"},{"name":"child2"}]},{"name":"test2"}]', EntityClass);
  print(list.length); // > 2
  print(list[0].name); // > test
  print(list[0].children[0].name); // > child1
}

Converting Maps and Lists<Map> to dart objects

Frameworks like Angular.dart come with several HTTP services which already transform the HTTP response to a map using JSON.encode. To use those encoded Maps or Lists use fromMap and fromMapList functions.

library example;

import 'package:dson/dson.dart';

@serializable
class EntityClass {
  String name;
  String _setted;

  @SerializedName("renamed")
  bool otherName;

  @ignore
  String notVisible;

  @DsonType(EntityClass) // This annotation is only neede for client side applications
  List<EntityClass> children;

  set setted(String s) => _setted = s;
  String get setted => _setted;
}

void main() {
  EntityClass object = fromMap({"name":"test","renamed":"blub","notVisible":"it is", "setted": "awesome"}, EntityClass);
  print(object.name); // > test
  print(object.otherName); // > blub
  print(object.notVisible); // > it is
  print(object.setted); // > awesome

  // to deserialize a list of items use [fromJsonList]
  List<EntityClass> list = fromMapList([{"name":"test", "children": [{"name":"child1"},{"name":"child2"}]},{"name":"test2"}], EntityClass);
  print(list.length); // > 2
  print(list[0].name); // > test
  print(list[0].children[0].name); // > child1
}

Libraries

dson