public class Business    {        [Key]        public int BusinessId { get; protected set; }        public string Name { get; set; }        public string LicenseNumber { get; set; }    }    public class Retail : Business    {        public string Address { get; set; }        public string City { get; set; }        public string State { get; set; }        public string ZIPCode { get; set; }    }        public class eCommerce : Business    {        public string URL { get; set; }    }public class BusinessesContext : DbContext    {        public DbSet<Business> Businesses { get; set; }               protected override void OnModelCreating(DbModelBuilder modelBuilder)        {            base.OnModelCreating(modelBuilder);            modelBuilder.Entity<Business>()                .Property(b=>b.BusinessId)                .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);            modelBuilder.Entity<Business>().ToTable("Business", "halower");            modelBuilder.Entity<Retail>().ToTable("Retail", "halower");            modelBuilder.Entity<eCommerce>().ToTable("eCommerce", "halower");        }    }

 private static void Main(string[] args)        {            using (var context = new BusinessesContext())            {                                 var retail = new Retail                {                    Name = "Shop and Save",                    LicenseNumber = "200C",                    Address = "101 Main",                    City = "Anytown",                    State = "TX",                    ZIPCode = "76106"                };                context.Businesses.Add(retail);                var web = new eCommerce                {                    Name = "BuyNow.com",                    LicenseNumber = "300AB",                    URL = "www.buynow.com"                };                context.Businesses.Add(web);                context.SaveChanges();            }            using (var context = new BusinessesContext())            {                Console.WriteLine("\n--- All Businesses ---");                foreach (var b in context.Businesses)                {                    Console.WriteLine("{0} (#{1})", b.Name, b.LicenseNumber);                }                Console.WriteLine("\n--- Retail Businesses ---");                //OfType<T>:根据指定类型筛选                foreach (var r in context.Businesses.OfType<Retail>())                {                    Console.WriteLine("{0} (#{1})", r.Name, r.LicenseNumber);                    Console.WriteLine("{0}", r.Address);                    Console.WriteLine("{0}, {1} {2}", r.City, r.State, r.ZIPCode);                }                Console.WriteLine("\n--- eCommerce Businesses ---");                foreach (var e in context.Businesses.OfType<eCommerce>())                {                    Console.WriteLine("{0} (#{1})", e.Name, e.LicenseNumber);                    Console.WriteLine("Online address is: {0}", e.URL);                }                Console.ReadKey();            }        }

  public abstract class Employee        {            public int EmployeeId { get; protected set; }            public string FirstName { get; set; }            public string LastName { get; set; }        }        public class FullTimeEmployee : Employee        {            public decimal? Salary { get; set; }        }        public class HourlyEmployee : Employee        {            public decimal? Wage { get; set; }        }        public class EmployeeContext: DbContext        {            public DbSet<Employee> Employees { get; set; }            protected override void OnModelCreating(DbModelBuilder modelBuilder)            {                base.OnModelCreating(modelBuilder);                modelBuilder.Entity<Employee>()                    .HasKey(e => e.EmployeeId)                    .Property(e => e.EmployeeId)                    .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);                modelBuilder.Entity<Employee>()                    .Map<FullTimeEmployee>(m => m.Requires("EmployeeType").HasValue(1))                    .Map<HourlyEmployee>(m => m.Requires("EmployeeType").HasValue(2));            }

      private static void Main(string[] args)        {            using (var context = new EmployeeContext())            {                var fte = new FullTimeEmployee                {                    FirstName = "Jane",                    LastName = "Doe",                    Salary = 71500M                };                context.Employees.Add(fte);                fte = new FullTimeEmployee                {                    FirstName = "John",                    LastName = "Smith",                    Salary = 62500M                };                context.Employees.Add(fte);                var hourly = new HourlyEmployee                {                    FirstName = "Tom",                    LastName = "Jones",                    Wage = 8.75M                };                context.Employees.Add(hourly);                context.SaveChanges();            }            using (var context = new EmployeeContext())            {                Console.WriteLine("--- All Employees ---");                foreach (var emp in context.Employees)                {                    bool fullTime = !(emp is HourlyEmployee);                    Console.WriteLine("{0} {1} ({2})", emp.FirstName, emp.LastName,                        fullTime ? "Full Time" : "Hourly");                }                Console.WriteLine("--- Full Time ---");                foreach (var fte in context.Employees.OfType<FullTimeEmployee>())                {                    Console.WriteLine("{0} {1}", fte.FirstName, fte.LastName);                }                Console.WriteLine("--- Hourly ---");                foreach (var hourly in context.Employees.OfType<HourlyEmployee>())                {                    Console.WriteLine("{0} {1}", hourly.FirstName, hourly.LastName);                }            }            Console.ReadKey();        }

 protected override void OnModelCreating(DbModelBuilder modelBuilder)            {                base.OnModelCreating(modelBuilder);                modelBuilder.Entity<Employee>()                    .HasKey(e => e.EmployeeId)                    .Property(e => e.EmployeeId)                    .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);                modelBuilder.Entity<FullTimeEmployee>()                    .Map(m =>                    {                        m.MapInheritedProperties();                        m.ToTable("FullTimeEmployee");                    });                modelBuilder.Entity<HourlyEmployee>()                    .Map(m =>                    {                        m.MapInheritedProperties();                        m.ToTable("HourlyEmployee");                    });            }