C# CodeFirst编程模型一

定义实体类型：

定义两个实体Menu和MenuCard，一个menu关联一个menucard，menucard包含对所有menu的引用。

 public class Menu
    {
        public int Id { get; set; }

        [StringLength(50)]
        public string Text { get; set; }
        public decimal Price { get; set; }
        public DateTime? Date { get; set; }
        public MenuCard MenuCard { get; set; }
        public int MenuCardId { get; set; }
    }

　　

public class MenuCard
    {
        public int Id { get; set; }
        public string Text { get; set; }
        public virtual ICollection<Menu> Menus { get; set; }
    }

　　创建数据上下文，新建类MenuContext派生于基类DbContext，使用模型构建器定义各个字段的约束和各表之间的级联关系，需要引用EntityFramework程序集。

 public class MenuContext:DbContext
    {
        public MenuContext():base(GetConnectionString())
        {
        }

        /// <summary>
        /// Get the connection string to connect database
        /// </summary>
        /// <returns>connection string</returns>
        private static string GetConnectionString()
        {
            ConnectionStringSettings settings = ConfigurationManager.ConnectionStrings["CodeFirst"];
            return settings.ConnectionString;
        }
       
        public DbSet<Menu> Menus { get; set; }
        public DbSet<MenuCard> MenuCards { get; set; }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Menu>().Property(m => m.Price).HasColumnType("money");
            modelBuilder.Entity<Menu>().Property(m => m.Date).HasColumnType("date");
            modelBuilder.Entity<Menu>().Property(m => m.Text).HasMaxLength(40).IsRequired();
            modelBuilder.Entity<Menu>().HasRequired(m => m.MenuCard).WithMany(c => c.Menus).HasForeignKey(m => m.MenuCardId);
            modelBuilder.Entity<MenuCard>().Property(c => c.Text).HasMaxLength(30).IsRequired();
            modelBuilder.Entity<MenuCard>().HasMany(c => c.Menus).WithRequired().WillCascadeOnDelete();
        }
    }

　　创建数据库，填充数据。数据库初始化实现了IDatabaseInitializer<TContext>接口，这个接口由CreateDatabaseIfNotExists、DropDatabaseAlways和DropDatabaseIfModelChanges实现，新建类MenuCardInitializer

public class MenuCardsInitializer:DropCreateDatabaseAlways<MenuContext>
    {
        protected override void Seed(MenuContext context)
        {
            var menuCards = new List<MenuCard>()
            {
                new MenuCard {
                    Text ="Soups",Menus=new List<Menu>(){
                    new Menu {
                        Text = "Baked Potatoe Soup",Price=4.80m,Date=DateTime.Parse("5/22/2016",System.Globalization.CultureInfo.InvariantCulture)
                    },
                    new Menu {
                        Text="Rib Eye Steak",Price=5.20m,Date=DateTime.Parse("5/21/2016",System.Globalization.CultureInfo.InvariantCulture)
                    }
                    }
                },
                new MenuCard {
                    Text ="Steaks",Menus=new List<Menu>() {
                    new Menu {
                    Text="New York Sirloin Steak",
                    Price=6.28m,Date=DateTime.Parse("5/20/2016",System.Globalization.CultureInfo.InvariantCulture)},
                    new Menu {
                    Text="Rib Eye Steak",Price=7.20m,Date=DateTime.Parse("5/19/2016",System.Globalization.CultureInfo.InvariantCulture)}
                    }
                }
            };
            menuCards.ForEach(c => context.MenuCards.Add(c));
        }
    }

　　在program类中运行：

class Program
    {
        static void Main(string[] args)
        {

            //CreateMenus().Wait();
            QueryMenu();
        }

        /// <summary>
        /// crwate data to test entity framework 
        /// </summary>
        /// <returns></returns>
        private static async Task CreateMenus()
        {
            using (var data = new MenuContext())
            {
                MenuCard card = data.MenuCards.Create();
                card.Text = "Soups";
                data.MenuCards.Add(card);
                Menu m = data.Menus.Create();
                m.Text = "Baked Potato Soup";
                m.Price = 4.80m;
                m.Date = new DateTime(2016, 5, 22);
                m.MenuCard = card;
                data.Menus.Add(m);
                Menu m1 = data.Menus.Create();
                m1.Text = "Cheddar Broccoli Soup";
                m1.Price = 5.06m;
                m1.Date = new DateTime(2016, 5, 21);
                m1.MenuCard = card;
                data.Menus.Add(m1);
                try
                {
                    data.SaveChanges();
                }
                catch(Exception ex)
                {
                    Console.WriteLine(ex.Message);
                }
            }
        }

        private static void QueryMenu()
        {
            using (var data = new MenuContext())
            {
                foreach (var card in data.MenuCards)
                {
                    Console.WriteLine(card.Text);
                    foreach (var menu in card.Menus)
                    {
                        Console.WriteLine("{0}-{1:d}", menu.Text, menu.Date);
                    }
                }
            }
        }
    }