Domain Layer

While adding new features, we will always start with the domain layer. The domain layer contains the entities and repositories/contracts of the feature. The domain layer is independent of the other layers and can be tested separately.

Getting started

Create a new folder named domain inside the scratch_notes folder.

Entities

1. Create a new file named scratch_note.dart inside the domain folder. This file will contain the entity class for the feature.

import 'package:freezed_annotation/freezed_annotation.dart';

part 'scratch_note.freezed.dart';
part 'scratch_note.g.dart';

@freezed
class ScratchNote with _$ScratchNote {
  const factory ScratchNote({
    required String id,
    required String userId,
    required String title,
    required DateTime createdAt,
  }) = _ScratchNote;

  factory ScratchNote.fromJson(Map<String, dynamic> json) =>
      _$ScratchNoteFromJson(json);

  factory ScratchNote.empty() => _ScratchNote(
        id: '',
        userId: '',
        title: '',
        createdAt: DateTime.now(),
      );
}

We're using the freezed package to create immutable classes. The ScratchNote class has four properties: id, userId, title, and createdAt. We also have a factory constructor to create an empty ScratchNote.

Repositories

Create a new file named i_scratch_note_repository.dart inside the domain folder. This file will contain the repository interface for the feature.

import 'package:fpdart/fpdart.dart';
import 'package:techshoi_app/features/core/domain/entities/failure.dart';
import 'package:techshoi_app/features/scratch_notes/domain/scratch_note.dart';

/// An abstract class representing the interface for a scratch note repository.
///
/// This interface defines the methods for interacting with scratch notes.
abstract class IScratchNoteRepository {
  /// Retrieves a list of scratch notes.
  ///
  /// Returns a [Future] that completes with an [Either] containing a [Failure]
  /// or a list of [ScratchNote] objects.
  Future<Either<Failure, List<ScratchNote>>> getScratchNotes();

  /// Adds a new scratch note.
  ///
  /// Returns a [Future] that completes with an [Either] containing a [Failure]
  /// or [Unit].
  Future<Either<Failure, Unit>> addScratchNote(String title);

  /// Updates an existing scratch note.
  ///
  /// Returns a [Future] that completes with an [Either] containing a [Failure]
  /// or [Unit].
  Future<Either<Failure, Unit>> updateScratchNote(ScratchNote note);

  /// Deletes a scratch note.
  ///
  /// Returns a [Future] that completes with an [Either] containing a [Failure]
  /// or [Unit].
  Future<Either<Failure, Unit>> deleteScratchNote(String noteId);

  /// Listens to changes in the scratch notes.
  ///
  /// Returns a [Stream] that emits an [Either] containing a [Failure]
  /// or a list of [ScratchNote] objects.
  Stream<Either<Failure, List<ScratchNote>>> listenToScratchNotes();
}

The IScratchNoteRepository interface defines the methods for interacting with scratch notes. The methods include getting, adding, updating, and deleting scratch notes. We also have a method to listen to changes in the scratch notes. We're using the fpdart package to handle errors. The Failure class , defined in the core module, is a class that represents a failure.