public class Student
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public int Age { get; set; }
    }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Student>().Property<DateTime>("InsertTime");
        }

    public class MyContext : DbContext
    {
        public DbSet<Student> Students { get; set; }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.UseSqlServer(@"server=(localdb)\MSSQLLocalDB;database=TestDb");
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Student>().Property<DateTime>("InsertTime");
        }
    }

        public void ConfigureServices(IServiceCollection services)
        {
            services.AddMvc();
            services.AddDbContext<MyContext>();
        }

        public static void Main(string[] args)
        {
            var host = CreateWebHostBuilder(args).Build();
            using(IServiceScope scope= host.Services.CreateScope())
            {
                MyContext c = scope.ServiceProvider.GetService<MyContext>();
                c.Database.EnsureCreated();
            }
            host.Run();
        }

    [Route("api/[action]")]
    public class TestController : Controller
    {
        readonly  MyContext context;
        public TestController(MyContext c) => context = c;

        [HttpPost]
        public ActionResult AddNew([FromBody]Student stu)
        {
            ……
        }

        [HttpGet]
        public JArray GetList()
        {
            ……
        }
    }

        [HttpPost]
        public ActionResult AddNew([FromBody]Student stu)
        {
            // 添加实体
            context.Students.Add(stu);
            // 设置影子属性
            context.Entry(stu).Property<DateTime>("InsertTime").CurrentValue = DateTime.Now;
            context.SaveChanges();
            return Ok("操作成功");
        }

        [HttpGet]
        public JArray GetList()
        {
            var q = from s in context.Students
                    select new
                    {
                        s.Id,
                        s.Name,
                        s.Age,
                        // 读取影子属性值
                        InsertTime = EF.Property<DateTime>(s, "InsertTime")
                    };
            JArray arr = new JArray();
            foreach (var s in q)
            {
                JObject obj = new JObject();
                obj.Add("id", new JValue(s.Id));
                obj.Add("name", new JValue(s.Name));
                obj.Add("age", new JValue(s.Age));
                obj.Add("add_time", new JValue(s.InsertTime));
                arr.Add(obj);
            }
            return arr;
        }

{
    "name":"李三跳",
    "age":52
}

[
    {
        "id": 1,
        "name": "什么鬼",
        "age": 29,
        "add_time": "2018-11-26T11:15:38.2012809"
    },
    {
        "id": 2,
        "name": "陈大扣",
        "age": 83,
        "add_time": "2018-11-26T11:21:07.5374308"
    },
    {
        "id": 3,
        "name": "李三跳",
        "age": 52,
        "add_time": "2018-11-26T12:41:51.758849"
    }
]