EF基础，从0开始：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data.Entity;
using System.ComponentModel.DataAnnotations;

namespace CodeFirstNewDatabase
{
    class Program
    {
        static void Main(string[] args)
        {
            using (var db = new BloggingContext())
            {
                Console.Write("Enter a name for a new Blog: ");
                var name = Console.ReadLine();

                var blog = new Blog { Name = name };
                db.Blogs.Add(blog);
                db.SaveChanges();

                var query = from b in db.Blogs
                            orderby b.Name
                            select b;

                Console.WriteLine("All blogs in the database:");
                foreach (var item in query)
                {
                    Console.WriteLine(item.Name);
                }
                Console.WriteLine("Press any key to exit...");
                Console.ReadKey();
            }
        }
    }
    public class Blog
    {
        public int BlogID { get; set; }
        public string Name { get; set; }
        public string Url { get; set; }

        public virtual IList<Post> Posts { get; set; }
    }
    public class Post
    {
        public int PostID { get; set; }
        public string Title { get; set; }
        public string Content { get; set; }

        public int BlogId { get; set; }
        public virtual Blog Blog { get; set; }
    }
    public class User
    {
        [Key]         // annotation: keyattribute
        public string Username { get; set; }
        public string Displayname { get; set; }
    }
    public class BloggingContext : DbContext
    {
         
        public DbSet<Blog> Blogs { get; set; }
        public DbSet<Post> Posts { get; set; }
        public DbSet<User> Users { get; set; }
        protected override void OnModelCreating(DbModelBuilder modelBuilder)           // fluent api: override onmodelcreating method
        {
            modelBuilder.Entity<User>()
                .Property(u => u.Displayname)
                .HasColumnName("Display_name");
        }

       
    }
}