Serialization

Source-generated serialization for Dart objects. This package uses package:source_gen to eliminate the time you spend writing boilerplate serialization code for your models. package:angel3_serialize also powers package:angel3_orm.

Usage

In your pubspec.yaml, you need to install the following dependencies:

dependencies:
  angel3_model: ^3.0.0
  angel3_serialize: ^4.0.0
dev_dependencies:
  angel3_serialize_generator: ^4.2.0
  build_runner: ^1.0.0

With the recent updates to package:build_runner, you can build models automatically, anywhere in your project structure, by running pub run build_runner build.

To tweak this: Build Config

If you want to watch for file changes and re-build when necessary, replace the build call with a call to watch. They take the same parameters.

Models

There are a few changes opposed to normal Model classes. You need to add a @serializable annotation to your model class to have it serialized, and a serializable model class's name should also start with a leading underscore.

In addition, you may consider using an abstract class to ensure immutability of models.

Rather you writing the public class, angel3_serialize does it for you. This means that the main class can have its constructors automatically generated, in addition into serialization functions.

For example, say we have a Book model. Create a class named _Book:

import 'package:angel3_model/angel_model.dart';
import 'package:angel3_serialize/angel3_serialize.dart';
import 'package:collection/collection.dart';
part 'book.g.dart';

@serializable
abstract class _Book extends Model {
  String get author;

  @SerializableField(defaultValue: '[Untitled]')
  String get title;

  String get description;

  int get pageCount;

  BookType get type;
}

/// It even supports enums!
enum BookType {
  fiction,
  nonFiction
}

The following file will be generated:

  • book.g.dart

Producing these classes:

  • Book: Extends or implements _Book; may be const-enabled.

  • BookSerializer: static functionality for serializing Book models.

  • BookFields: The names of all fields from the Book model, statically-available.

  • BookEncoder: Allows BookSerializer to extend Codec<Book, Map>.

  • BookDecoder: Also allows BookSerializer to extend Codec<Book, Map>.

And the following other features:

  • bookSerializer: A top-level, const instance of BookSerializer.

  • Book.toString: Prints out all of a Book instance's fields.

Serialization

You can use the generated files as follows:

myFunction() {
  var warAndPeace = new Book(
    author: 'Leo Tolstoy',
    title: 'War and Peace',
    description: 'You will cry after reading this.',
    pageCount: 1225
  );

  // Easily serialize models into Maps
  var map = BookSerializer.toMap(warAndPeace);

  // Also deserialize from Maps
  var book = BookSerializer.fromMap(map);
  print(book.title); // 'War and Peace'

  // For compatibility with `JSON.encode`, a `toJson` method
  // is included that forwards to `BookSerializer.toMap`:
  expect(book.toJson(), map);

  // Generated classes act as value types, and thus can be compared.
  expect(BookSerializer.fromMap(map), equals(warAndPeace));
}

As of 2.0.2, the generated output also includes information about the serialized names of keys on your model class.

  myOtherFunction() {
    // Relying on the serialized key of a field? No worries.
      map[BookFields.author] = 'Zora Neale Hurston';
  }

Customizing Serialization

Currently, these serialization methods are supported:

  • to Map

  • to JSON

  • to TypeScript definitions

You can customize these by means of serializers:

@Serializable(serializers: const [Serializers.map, Serializers.json])
class _MyClass extends Model {}

Subclasses

angel3_serialize pulls in fields from parent classes, as well as implemented interfaces, so it is extremely easy to share attributes among model classes:

import 'package:angel3_serialize/angel3_serialize.dart';
part 'subclass.g.dart';

@serializable
class _Animal {
  @notNull
  String genus;
  @notNull
  String species;
}

@serializable
class _Bird extends _Animal {
  @DefaultsTo(false)
  bool isSparrow;
}

var saxaulSparrow = Bird(
  genus: 'Passer',
  species: 'ammodendri',
  isSparrow: true,
);

Aliases

Whereas Dart fields conventionally are camelCased, most database columns tend to be snake_cased. This is not a problem, because we can define an alias for a field.

By default angel3_serialize will transform keys into snake case. Use alias to provide a custom name, or pass autoSnakeCaseNames: false to the builder;

@serializable
abstract class _Spy extends Model {
  /// Will show up as 'agency_id' in serialized JSON.
  ///
  /// When deserializing JSON, instead of searching for an 'agencyId' key,
  /// it will use 'agency_id'.
  ///
  /// Hooray!
  String agencyId;

  @SerializableField(alias: 'foo')
  String someOtherField;
}

You can also override autoSnakeCaseNames per model:

@Serializable(autoSnakeCaseNames: false)
abstract class _OtherCasing extends Model {
  String camelCasedField;
}

Excluding Keys

In pratice, there may keys that you want to exclude from JSON. To accomplish this, simply annotate them with @exclude:

@serializable
abstract class _Whisper extends Model {
  /// Will never be serialized to JSON
  @SerializableField(exclude: true)
  String secret;
}

There are times, however, when you want to only exclude either serialization or deserialization, but not both. For example, you might want to deserialize passwords from a database without sending them to users as JSON.

In this case, use canSerialize or canDeserialize:

@serializable
abstract class _Whisper extends Model {
  /// Will never be serialized to JSON
  ///
  /// ... But it can be deserialized
  @SerializableField(exclude: true, canDeserialize: true)
  String secret;
}

Required Fields

It is easy to mark a field as required:

@serializable
abstract class _Foo extends Model {
  @SerializableField(isNullable: false)
  int myRequiredInt;

  @SerializableField(isNullable: false, errorMessage: 'Custom message')
  int myOtherRequiredInt;
}

The given field will be marked as @required in the generated constructor, and serializers will check for its presence, throwing a FormatException if it is missing.

Adding Annotations to Generated Classes

There are times when you need the generated class to have annotations affixed to it:

@Serializable(
  includeAnnotations: [
    Deprecated('blah blah blah'),
    pragma('something...'),
  ]
)
abstract class _Foo extends Model {}

Custom Serializers

package:angel3_serialize does not cover every known Dart data type; you can add support for your own. Provide serializer and deserializer arguments to @SerializableField() as you see fit.

They are typically used together. Note that the argument to deserializer will always be dynamic, while serializer can receive the data type in question.

In such a case, you might want to also provide a serializesTo argument. This lets the generator, as well as the ORM, apply the correct (de)serialization rules and validations.

DateTime _dateFromString(s) => s is String ? HttpDate.parse(s) : null;
String _dateToString(DateTime v) => v == null ? null : HttpDate.format(v);

@serializable
abstract class _HttpRequest {
  @SerializableField(
    serializer: #_dateToString,
    deserializer: #_dateFromString,
    serializesTo: String)
  DateTime date;
}

Nesting

angel3_serialize also supports a few types of nesting of @serializable classes:

  • As a class member, ex. Book myField

  • As the type argument to a List, ex. List<Book>

  • As the second type argument to a Map, ex. Map<String, Book>

In other words, the following are all legal, and will be serialized/deserialized. You can use either the underscored name of a child class (ex. _Book), or the generated class name (ex Book):

@serializable
abstract class _Author extends Model {
  List<Book> books;
  Book newestBook;
  Map<String, Book> booksByIsbn;
}

If your model (Author) depends on a model defined in another file (Book), then you will need to generate book.g.dart before, author.g.dart, in a separate build action. This way, the analyzer can resolve the Book type.

ID and Dates

This package will automatically generate id, createdAt, and updatedAt fields for you, in the style of an Angel3 Model. This will automatically be generated, only for classes extending Model.

Binary Data

package:angel3_serialize also handles Uint8List fields, by means of serialization to and from base64 encoding.

TypeScript Definitions

It is quite common to build frontends with JavaScript and/or TypeScript, so why not generate typings as well?

To accomplish this, add Serializers.typescript to your @Serializable() declaration:

@Serializable(serializers: const [Serializers.map, Serializers.json, Serializers.typescript])
class _Foo extends Model {}

The aforementioned _Author class will generate the following in author.d.ts:

interface Author {
  id: string;
  name: string;
  age: number;
  books: Book[];
  newest_book: Book;
  created_at: any;
  updated_at: any;
}
interface Library {
  id: string;
  collection: BookCollection;
  created_at: any;
  updated_at: any;
}
interface BookCollection {
  [key: string]: Book;
}

Fields with an @Exclude() that specifies canSerialize: false will not be present in the TypeScript definition. The rationale for this is that if a field (i.e. password) will never be sent to the client, the client shouldn't even know the field exists.

Constructor Parameters

Sometimes, you may need to have custom constructor parameters, for example, when using depedency injection frameworks. For these cases, angel3_serialize can forward custom constructor parameters.

The following:

@serializable
abstract class _Bookmark extends _BookmarkBase {
  @SerializableField(exclude: true)
  final Book book;

  int get page;
  String get comment;

  _Bookmark(this.book);
}

Generates:

class Bookmark extends _Bookmark {
  Bookmark(Book book,
      {this.id,
      this.page,
      this.comment,
      this.createdAt,
      this.updatedAt})
      : super(book);

  @override
  final String id;

  // ...
}
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