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lib/13/go/raw_book/src/data/author.dart

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+// Copyright 2021, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'book.dart';
+
+class Author {
+  final int id;
+  final String name;
+  final books = <Book>[];
+
+  Author(this.id, this.name);
+}

lib/13/go/raw_book/src/data/book.dart

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+// Copyright 2021, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'author.dart';
+
+class Book {
+  final int id;
+  final String title;
+  final Author author;
+  final bool isPopular;
+  final bool isNew;
+
+  Book(this.id, this.title, this.isPopular, this.isNew, this.author);
+}

lib/13/go/raw_book/src/data/library.dart

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+// Copyright 2021, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'author.dart';
+import 'book.dart';
+
+final libraryInstance = Library()
+  ..addBook(
+      title: 'Left Hand of Darkness',
+      authorName: 'Ursula K. Le Guin',
+      isPopular: true,
+      isNew: true)
+  ..addBook(
+      title: 'Too Like the Lightning',
+      authorName: 'Ada Palmer',
+      isPopular: false,
+      isNew: true)
+  ..addBook(
+      title: 'Kindred',
+      authorName: 'Octavia E. Butler',
+      isPopular: true,
+      isNew: false)
+  ..addBook(
+      title: 'The Lathe of Heaven',
+      authorName: 'Ursula K. Le Guin',
+      isPopular: false,
+      isNew: false);
+
+class Library {
+  final List<Book> allBooks = [];
+  final List<Author> allAuthors = [];
+
+  void addBook({
+    required String title,
+    required String authorName,
+    required bool isPopular,
+    required bool isNew,
+  }) {
+    var author = allAuthors.firstWhere(
+      (author) => author.name == authorName,
+      orElse: () {
+        final value = Author(allAuthors.length, authorName);
+        allAuthors.add(value);
+        return value;
+      },
+    );
+    var book = Book(allBooks.length, title, isPopular, isNew, author);
+
+    author.books.add(book);
+    allBooks.add(book);
+  }
+
+  List<Book> get popularBooks => [
+        ...allBooks.where((book) => book.isPopular),
+      ];
+
+  List<Book> get newBooks => [
+        ...allBooks.where((book) => book.isNew),
+      ];
+}