dart_mappable 0.3.8

Serialize / deserialize dart objects effortlessly, without any boilerplate code or annotations.

Imagine a serialization package with:

• NO boilerplate code (Nothing at all, ZERO lines of code)
• NO annotations ("Don't @ me...")
• NO minified/uglified generated files
• NO extra dependencies (Yes, not even to this package)

while still being able to

• decode & encode json
• come with built-in type & null-safety
• be fully configurable
• support custom types

Sounds too good to be true? Not anymore.

Dart Mappable

Have a look at the example!

Get Started

This package is designed to be purely used as a dev_dependency. No need to import this package anywhere in your code. To get started, add the following lines to your pubspec.yaml:

dev_dependencies:
  dart_mappable: ^0.3.8
  build_runner: ^1.12.2

Next, create a build.yaml in the root directory of your package and add this snippet:

targets:
  $default:
    builders:
      dart_mappable:
        generate_for:
          - lib/main.dart # modify this if you have a different entry point

In order to generate the serialization code, run the following command:

pub run build_runner build

You'll need to re-run code generation each time you are making changes to your code. So for development time, use watch like this

pub run build_runner watch

This will generate a .g.dart file for each of your entry points specified in the build.yaml file. Last step is to import the generated files wherever you want / need them.

Hint: This package will generate clean, formatted, and easy to understand code. Have a look at the generated files. I guarantee you won't be drowned in uglified code.

TODOs

• More Encoding / Decoding options
• Unmapped properties
• Annotations (Optional!)

Builder Config

Instead of clustering your code with annotations, this package uses builder options inside your build.yaml file to specify how your classes should behave when serializing / deserializing. All options are optional!

targets:
  $default:
    builders:
      dart_mappable:
        generate_for:
          - lib/main.dart
          - lib/models.dart # multiple independent entry files
        options:

          # use only one of (exclude, include) or none, which then generates code for all classes
          exclude: [ClassA, ClassB] # ignores specific classes, generates code for all else
          include: [ClassC, ClassD] # generates code for specified classes, ignores all else

          # the case style for the map keys, defaults to 'none'
          caseStyle: none # or 'camelCase', 'snakeCase', etc.
          # the case style for stringified enum values, defaults to 'none'
          enumCaseStyle: none # or 'camelCase', 'snakeCase', etc.
          # if true removes all map keys with null values
          ignoreNull: false # or true
          # used as property name for type discriminators, defaults to '_type'
          discriminator: isOfType
          
          # overwrite options for specific libraries
          libraries: 

            # referenced by its entry point (also for implicit libraries)
            lib/main.dart: 
              include: [ClassA] # here: include only class 'ClassA'

              # overwrite options for specific classes
              classes: 
                ClassA: # name of the class
                  constructor: decode # specify a named constructor to use (instead of using the default)
                  caseStyle: camelCase # overwrite the caseStyle
                  discriminatorValue: my-class # set a custom value for the discriminator property
                  fields: # overwrite the string mapping for specific fields
                    someField: _my+special:json_key
              
              # overwrite options for specific enums
              enums:
                MyEnum:
                  caseStyle: snakeCase # overwrite the caseStyle
            
            # referenced by its name
            models: 
              exclude: [] # here: include everything
              ignoreNull: true # here: overwrite property to remove keys with null values
              caseStyle: custom(lc,+) # here: set a custom case style (see below)

Case Styles

You can specify the case style for the json keys and your stringified enum values. Choose one of the existing styles or spefify a custom one.

Currently supported are:

none / unmodified: keeps your field names as the are (default)
camelCase: myFieldName -> myFieldName (dart default)
pascalCase: myFieldName -> MyFieldName
snakeCase: myFieldName -> my_field_name
paramCase: myFieldName -> my-field-name
lowerCase: myFieldName -> myfieldname
upperCase: myFieldName -> MYFIELDNAME

You can also specify a custom case style using the custom(ab,c) syntax.

• The letters before the comma define how to transform each word of a field name. They can be either l for lowerCase, u for upperCase, or c for capitalCase. When using only one letter, it is applied to all words. When using two letters, the first one is applied to only the first word and the second one to all remaining words.
• The one letter after the comma defines the seperator between each word, like _ or -. This can be any character or empty.

Here are some examples that can be achieved using this syntax:

custom(u,_): myFieldName -> MY_FIELD_NAME
custom(uc,+): myFieldName -> MY+Field+Name
custom(cl,): myFieldName -> Myfieldname

Utilize Constructors

There exist a lot of custom use cases, when it comes to mapping any object. Common ones include renaming fields, ignoring fields, computing values, or custom date or number formats. Instead of providing custom tailored serialization options for each use-case, this package utilizes the power of constructor arguments to cover all of them. Thereby, you keep full control over your models, while writing pure and easy dart code.

How does that work exactly: When analysing your code, dart_mappable never looks at the fields of your model, but rather only at the constructor arguments; What you do with them - writing to fields, renaming, etc. - is up to your model's implementation. To illustrate this, here are some examples for the above mentioned use cases:

class Person {
  String name;
  int age;
    
  // basic example, nothing special going on
  Person.base(this.name, this.age);

  // renamed argument, will be 'years': ... in json
  Person.renamed(this.name, int years) : age = years;
  // when renaming arguments, make sure to always have a matching getter for serialization *
  int get years => age;
  
  // ignores the age field completely
  Person.ignored(this.name);
 
  // computed name value
  Person.computed(String firstName, String lastName, this.age) : name = '$firstName $lastName';
  // again: have matching getters for all arguments, reversing the computed value
  String get firstName => name.split(' ')[0];
  String get lastName => name.split(' ')[1];
}

class Event {
  DateTime date;

  // custom formatting as unix timestamp
  Car.format(int timestamp) : date = DateTime.fromMillisecondsSinceEpoch(timestamp);
  int get timestamp => date.millisecondsSinceEpoch;
}

Tip regarding the matching getters: Not-having them won't break your code. However this will lead to desynched serialization (keys missing in your json) and eventually to errors when trying to deserialize back.

Tip: dart_mappable will always use the first constructor it sees, but you can set a specific named constructor by using the 'constructor' option in the build.yaml file.

Custom Types

You can create custom mappers to serialize / deserialize custom types that are not part of the generated code like this:

class CustomStringMapper extends BaseMapper<String> {
  // don't mind the syntax here for now
  @override
  Function get decoder => (dynamic value) {
    return (value as String).substring(1);
  };
  
  @override
  dynamic encode(String self) {
    return '_$self';
  }
}

// then, somewhere early in your code (e.g. main function)
Mapper.use(CustomStringMapper());

Instead of extending BaseMapper<T> you can also directly extend Mapper<T>; This will give you a few more methods to override, which will enable Mapper.isEqual and Mapper.asString on this type.

Curious about the strange syntax for the decoder function? This is necessary, in order to handle generic classes with type attributes.

class GenericBox<T> {
  T content;
  GenericBox(this.content);
}

class CustomGenericMapper extends BaseMapper<GenericBox> { // only use the base type here

  @override
  Function get decoder => <T>(dynamic value) { // specify the decoder as a generic function
    return GenericBox<T>(Mapper.fromValue<T>(value)); // use the type parameter in your decoding logic
  };
  
  @override
  dynamic encode(GenericBox self) { // no need for type parameters here
    return Mapper.toValue(self.content);
  }

  // in case of generic types, we also must specify a type factory. This is a special type of 
  // function used internally to construct generic instances of your type.
  // specify any type arguments in alignment to the decoder function
  @override
  Function get typeFactory => <T>(f) => f<GenericBox<T>>();
}

// don't forget
Mapper.use(CustomGenericMapper());

Lists, Sets and Maps

We support lists, sets and maps out of the box, without any special syntax, workarounds or hacks. Just use Mapper.fromJson as you normally would:

class Dog with Mappable {
  String name;
  Dog(this.name);
}

class Box<T> with Mappable {
  T content;
  Box(this.content);
}

void main() {

  // simple list
  List<int> nums = Mapper.fromJson('[2, 4, 105]');
  print(nums); // [2, 4, 105]

  // set of objects
  Set<Dog> dogs = Mapper.fromJson('[{"name": "Thor"}, {"name": "Lasse"}, {"name": "Thor"}]');
  print(dogs); // {Dog(name: Thor), Dog(name: Lasse)}

  // or more complex lists, like generics
  List<Box<double>> boxes = Mapper.fromJson('[{"content": 0.1}, {"content": 12.34}]');
  print(boxes); // [Box(content: 0.1), Box(content: 12.34)]
}

There is also the Mapper.fromIterable method. This can be used if you already have a list of dynamic objects instead of the raw json string. Additionally this can get handy to decode a dynamic list of partly-encoded values:

List<double> myNumbers = Mapper.fromIterable([2.312, '1.32', 500, '1e4']);
print(myNumbers); // [2.312, 1.32, 500.0, 10000.0]

Non-Trivial Maps

We also support decoding of non-trivial maps. Although the use-cases might be rare, you can decode to something other than a map of string keys like this:

var encodedMap = {
  {'name': 'Bonny'}: 1,
  {'name': 'Clyde'}: 5,
};

Map<Dog, int> treatsPerDog = Mapper.fromValue(encodedMap);
print(treatsPerDog[Dog('Clyde')]!); // 5

var myMap = Mapper.toValue(treatsPerDog);
print(myMap); // {{name: Bonny}: 1, {name: Clyde}: 5}

Make sure to do mixin Mapper on your key class, in order to enable easy property access

Since json only supports string keys, we can't do Mapper.fromJson or Mapper.toJson on these maps. You would have to decode / encode your keys and values separately.

Custom Mappers

For special Iterable and Map types, you can of course specify CustomMappers as described in the previous section. However, we provide ready-to-use IterableMapper and MapMapper to make your life a little bit easier:

For both you have to provide

1. a factory function, which converts a generic iterable / map to your special implementation,
2. a type factory, similar to the one used in generic custom mappers.

Mapper.use(IterableMapper<HashSet>(
  <T>(Iterable<T> i) => HashSet.of(i),
  <T>(f) => f<HashSet<T>>(),
));

Mapper.use(MapMapper<HashMap>(
  <K, V>(Map<K, V> m) => HashMap.of(m),
  <K, V>(f) => f<HashMap<K, V>>(),
));

HashSet<Brand> brands = Mapper.fromJson('["toyota", "audi", "audi"]');
print(brands); // {Brands.Toyota, Brands.Audi}

Polymorphism and Discriminators

A common pattern that you might want to use for your classes is polymorphism. As a simple example see the classes below.

abstract class Animal with Mappable {
  String name;
  Animal(this.name);
}

class Cat extends Animal {
  String color;
  Cat(String name, this.color) : super(name);
}

class Dog extends Animal {
  int age;
  Dog(String name, this.age) : super(name);
}

Now when we want to encode a Home object, the pet property can either be a Cat or a Dog. To make sure that this information isn't lost when converting to json, we need to add a discriminator property, that keeps track of the specific type of the pet.

By default this property is named _type, but you can change it in the build configuration. The value of this property will default to the name of the class, but you can change this as well with the discriminatorValue property. Make sure to specify the discriminator property on the base class - Animal in our example - and the discriminatorValue property on each of the child classes - Cat and Dog in our case.

void main() {
  // encode a polymorphic class
  String catJson = Mapper.toJson(Cat('Judy', 'Black'));
  print(catJson); // {"name":"Judy","color":"Black","_type":"Cat"}

  Animal myPet = Mapper.fromJson(catJson); // implicit decoding as an 'Animal'
  print(myPet.runtimeType); // Cat

  // explicit decoding also works as usual without a discriminator
  Cat myCat = Mapper.fromJson('{"name": "Kitty", "color": "Brown"}');
  print(myCat.name); // Kitty
}