Flutter application

The client use case validates with Book.create, then saves. The server id replaces the local one.

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The client use case has the same shape as the server use case: a command, a clock, an id generator, and Book.create. The difference is what save means.

On the server, save stores the book whose id the use case just minted. On the client, SaveBookInput has no id field. The server mints the id that gets stored. The client still calls Book.create so a blank title throws before any HTTP call. The id passed into create is only there because a book has an identity. ServerpodBookRepository.save ignores it and returns the book from BookDto.

Create lib/application/book/save_book_command.dart:

dart

import 'package:shelf_flutter/domain/book/reading_status.dart';

class SaveBookCommand {
  const SaveBookCommand({
    required this.title,
    required this.authorName,
    required this.status,
  });

  final String title;
  final String authorName;
  final ReadingStatus status;
}

Create lib/application/book/save_book_use_case.dart:

dart

import 'package:shelf_flutter/application/book/save_book_command.dart';
import 'package:shelf_flutter/application/ports/clock.dart';
import 'package:shelf_flutter/application/ports/id_generator.dart';
import 'package:shelf_flutter/domain/book/book.dart';
import 'package:shelf_flutter/domain/book/book_repository.dart';

/// Validates with [Book.create], then stores through the port.
///
/// The id used for validation is replaced by the id the server returns.
class SaveBookUseCase {
  const SaveBookUseCase(
    this._books, {
    required this.clock,
    required this.ids,
  });

  final BookRepository _books;
  final Clock clock;
  final IdGenerator ids;

  Future<Book> execute(SaveBookCommand command) {
    final draft = Book.create(
      id: ids.newId(),
      title: command.title,
      authorName: command.authorName,
      status: command.status,
      createdAt: clock.now(),
    );
    return _books.save(draft);
  }
}

lib/application/book/list_books_use_case.dart:

dart

import 'package:shelf_flutter/domain/book/book.dart';
import 'package:shelf_flutter/domain/book/book_repository.dart';

class ListBooksUseCase {
  const ListBooksUseCase(this._books);

  final BookRepository _books;

  Future<List<Book>> execute() => _books.list();
}

Copy the ports into lib/application/ports/. They are application ports, not widgets.

clock.dart:

dart

abstract interface class Clock {
  DateTime now();
}

class SystemClock implements Clock {
  const SystemClock();

  @override
  DateTime now() => DateTime.now().toUtc();
}

id_generator.dart:

dart

import 'package:uuid/uuid.dart';

abstract interface class IdGenerator {
  String newId();
}

class UuidIdGenerator implements IdGenerator {
  const UuidIdGenerator();

  static const _uuid = Uuid();

  @override
  String newId() => _uuid.v4();
}

Do not import package:shelf_client in this folder. SaveBookCommand.status is the domain ReadingStatus, not ReadingStatusWire.

Next: the data layer.