/* This is a modified version of the code created by r f. - https://code.sololearn.com/c39j1vOyFh4y/?ref=app - This modified version contains quite a number of revisions. Description in the comments to the code */ using System; using System.Collections.Generic; using System.Linq; using static System.Console; namespace SoloLearn { //Entities class Book { public Book() { } public Book(int id, string title, List authors = null) { Id = id; Title = title; Authors = authors; Authors = authors == null ? new List() : authors; } public int Id { get; set; } public string Title { get; set; } public List Authors { get; set; } = new List(); } class Author { public Author() { } public Author(int id, string name, List books = null) { Id = id; Name = name; Books = books == null ? new List() : books; } public int Id { get; set; } public string Name { get; set; } public List Books { get; set; } = new List(); } //Simple Database context /* Implementing a many-to-many * relationship between tables: * Books(BookSet) and * Authors(AuthorSet) */ class Database { public Database() { new Initializing(this); } public List Books { get; set; } = new List(); public List Authors { get; set; } = new List(); } //Database context initializing class Initializing { Database db; public Initializing(Database db) { this.db = db; Seed(); } //initial values for database tables void Seed() { this.db.Books = new List { new Book(1, "Learning C"), new Book(2, "Learning C++"), new Book(3, "Learning C#"), new Book(4, "Learning HTML5 / CSS3"), new Book(5, "Learning JavaScript"), new Book(6, "Learning PHP"), new Book(7, "Learning Java") }; this.db.Authors = new List { new Author(1, "Adam Tree"), new Author(2, "Bob Skywalker"), new Author(3, "Clod Sun"), new Author(4, "David Water") }; var booksToAuthors = new int[][] { new[] { 1, 2, 3 }, new[] { 2 }, new[] { 3, 2 }, new[] { 4 }, new[] { 1 }, new[] { 2 }, new[] { 3, 2 } }; for (int i = 0; i < booksToAuthors.Length; i++) { db.Books[i].Authors = db.Authors.Where( author => { var isMatch = booksToAuthors[i].Contains(author.Id); if (isMatch) author.Books.Add(db.Books[i]); return isMatch; } ).ToList(); } } } /////////// TESTING ////////////// class Program { static void Log(string message, bool append = false) { if (append) Write(message); else WriteLine(message); } static void Main(string[] args) { Database db = new Database(); //READ ///////////// //Get all books //////// Log("GET ALL BOOKS"); db.Books.ForEach(book => { Log($"\n\"{book.Title}\"\n\t - by ", true); book.Authors.ForEach(author => { Log($"{author.Name}{(author == book.Authors.Last() ? "\n" : ", ")}", true); }); }); //Get the books of a certain author ////////////// Log("\nGet all the books by Bob Skywalker".ToUpper()); //First way db.Books .Where( b => b.Authors.Any(a => a.Name == "Bob Skywalker") ).ToList() .ForEach(book => Log($"\t - {book.Title}")); Log("\nGet all the books by Adam Tree".ToUpper()); //Second way db.Authors .FirstOrDefault(a => a.Name == "Adam Tree")? .Books.ForEach(book => Log($"\t - {book.Title}")); ///// To be continued... } } }

Database Context Imitation - Revised