SaveChanges()不会在Visual Studio c#中更新实际的表数据

不管什么原因，这段代码只能在程序运行时工作。它更新db中的一行。，并将其打印到列表框中。但是一旦退出，数据库中就没有该表的表数据了。它根本不会保存更改。

private void button1_Click(object sender, EventArgs e)
    {
        Database1Entities db = new Database1Entities();
        var st = new Student { StudentID = 1, StudentName = "Jack" };

        db.Students.Attach(st);
        db.Students.Add(st);
        db.SaveChanges();
        foreach (Student s in db.Students)
            listBox1.Items.Add(s.StudentName);
    }

编辑-这是我的上下文:

//--------------------------------------------------------------------------
----
// <auto-generated>
//     This code was generated from a template.
//
//     Manual changes to this file may cause unexpected behavior in your application.
//     Manual changes to this file will be overwritten if the code is regenerated.
// </auto-generated>
//------------------------------------------------------------------------------
namespace WindowsFormsApplication4
{
    using System;
    using System.Data.Entity;
    using System.Data.Entity.Infrastructure;
    public partial class Database1Entities1 : DbContext
    {
        public Database1Entities1()
            : base("name=Database1Entities1")
        {
        }
        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            throw new UnintentionalCodeFirstException();
        }
        public virtual DbSet<Student> Students { get; set; }
    }
}