Custom serialization

For most purposes, you will want to use Serverpod's native serialization. However, there may be cases where you want to serialize more advanced objects. With Serverpod, you can pass any serializable objects as long as they conform to three simple rules:

1. Your objects must have a method called toJson() which returns a JSON serialization of the object.

   Map<String, dynamic> toJson() {
   return {
       name: 'John Doe',
   };
   }

2. There must be a constructor or factory called fromJson(), which takes a JSON serialization as parameters.

   factory ClassName.fromJson(
   Map<String, dynamic> json,
   ) {
   return ClassName(
       name: json['name'] as String,
   );
   }

3. There must be a method called copyWith(), which returns a new instance of the object with the specified fields replaced.

   tip

   In the framework, copyWith() is implemented as a deep copy to ensure immutability. We recommend following this approach when implementing it for custom classes to avoid unintentional side effects caused by shared mutable references.

   ClassName copyWith({
     String? name,
   }) {
     return ClassName(
       name: name ?? this.name,
     );
   }

4. You must declare your custom serializable objects in the config/generator.yaml file in the server project, the path needs to be accessible from both the server package and the client package.

   ...
   extraClasses:
   - package:my_project_shared/my_project_shared.dart:ClassName

Setup example

We recommend creating a new dart package specifically for sharing these types of classes and importing it into the server and client pubspec.yaml. This can easily be done by running $ dart create -t package <my_project>_shared in the root folder of your project.

Your folder structure should then look like this:

├── my_project_client
├── my_project_flutter
├── my_project_server
├── my_project_shared

Then you need to update both your my_project_server/pubspec.yaml and my_project_client/pubspec.yaml and add the new package as a dependency.

dependencies:
  ...
  my_project_shared:
    path: ../my_project_shared
  ...

Now you can create your custom class in your new shared package:

class ClassName {
  String name;
  ClassName(this.name);

  toJson() {
    return {
      'name': name,
    };
  }

  factory ClassName.fromJson(
    Map<String, dynamic> jsonSerialization,
  ) {
    return ClassName(
      jsonSerialization['name'],
    );
  }
}

After adding a new serializable class, you must run serverpod generate. You are now able to use this class in your endpoints and leverage the full serialization/deserialization management that comes with Serverpod.

In your server project, you can create an endpoint returning your custom object.

import 'package:relation_test_shared/relation_test_shared.dart';
import 'package:serverpod/serverpod.dart';

class ExampleEndpoint extends Endpoint {
  Future<ClassName> getMyCustomClass(Session session) async {
    return ClassName(
      'John Doe',
    );
  }
}

Custom object with Freezed

Serverpod also has support for using custom classes created with the Freezed package.

import 'package:freezed_annotation/freezed_annotation.dart';

part 'freezed_custom_class.freezed.dart';
part 'freezed_custom_class.g.dart';

@freezed
class FreezedCustomClass with _$FreezedCustomClass {
  const factory FreezedCustomClass({
    required String firstName,
    required String lastName,
    required int age,
  }) = _FreezedCustomClass;

  factory FreezedCustomClass.fromJson(
    Map<String, Object?> json,
  ) =>
      _$FreezedCustomClassFromJson(json);
}

In the config/generator.yaml, you declare the package and the class:

extraClasses:
  - package:my_shared_package/my_shared_package.dart:FreezedCustomClass

Custom Object with ProtocolSerialization

If you need certain fields to be omitted when transmitting to the client-side, your server-side custom class should implement the ProtocolSerialization interface. This requires adding a method named toJsonForProtocol(). Serverpod will then use this method to serialize your object for protocol communication. If the class does not implement ProtocolSerialization, Serverpod defaults to using the toJson() method.

Implementation Example

Here’s how you can implement it:

class CustomClass implements ProtocolSerialization {
  final String? value;
  final String? serverSideValue;

  .......

  // Serializes fields specifically for protocol communication
  Map<String, dynamic> toJsonForProtocol() {
    return {
      "value":value,
    };
  }

  // Serializes all fields, including those intended only for server-side use
  Map<String, dynamic> toJson() {
    return {
      "value": value,
      "serverSideValue": serverSideValue,
    };
  }
}

This structure ensures that sensitive or server-only data is not exposed to the client, enhancing security and data integrity.

Importantly, this implementation is not required for client-side custom models.