using System.ComponentModel.DataAnnotations;

namespace EFDemo4
{
    public class User
    {
        [Key]
        public int Id { get; set; }
        public string Name { get; set; }
    }
}

using System.Data.Entity;

namespace EFDemo4
{
    public class TestDBContext: DbContext
    {
        public TestDBContext()
            : base("name=TestDB3")
        {

        }
        public DbSet<User> Users { get; set; }
    }
}

using System;
using System.Data.Entity;
using System.Linq;
using System.Windows.Forms;

namespace EFDemo4
{
    public partial class Form1 : Form
    {
        TestDBContext entity = new TestDBContext();
        public Form1()
        {
            InitializeComponent();
        }

        /// <summary>
        /// 新增
        /// </summary>
        private void Add()
        {
            User model = new User()
            {
                Name = DateTime.Now.ToString("yyyy-MM-dd hh:mm:ss")
            };
            entity.Users.Add(model);
            entity.SaveChanges();
            Query();
        }

        /// <summary>
        /// 删除
        /// </summary>
        private void Delete()
        {
            if (listBox1.SelectedItem == null)
            {
                return;
            }
            int id = Convert.ToInt32(listBox1.SelectedItem.ToString().Split(‘-‘)[0]);
            User model = entity.Users.Where(a => a.Id == id).FirstOrDefault();
            if (model != null)
            {
                entity.Entry(model).State = EntityState.Deleted;
                entity.SaveChanges();
                Query();
            }
        }

        /// <summary>
        /// 修改
        /// </summary>
        private void Edit()
        {
            if (listBox1.SelectedItem == null)
            {
                return;
            }
            int id = Convert.ToInt32(listBox1.SelectedItem.ToString().Split(‘-‘)[0]);
            User model = entity.Users.Where(a => a.Id == id).FirstOrDefault();
            if (model != null)
            {
                model.Name = DateTime.Now.ToString("yyyy-MM-dd hh:mm:ss");
                entity.Entry(model).State = EntityState.Modified;
                entity.SaveChanges();
                Query();
            }
        }

        /// <summary>
        /// 查询
        /// </summary>
        private void Query()
        {
            listBox1.Items.Clear();
            var expr = from p in entity.Users select p;
            foreach (var item in expr)
            {
                listBox1.Items.Add(string.Format("{0}-{1}", item.Id, item.Name));
            }
        }

        private void toolStripButton1_Click(object sender, EventArgs e)
        {
            Add();
        }

        private void toolStripButton4_Click(object sender, EventArgs e)
        {
            Edit();
        }

        private void toolStripButton3_Click(object sender, EventArgs e)
        {
            Delete();
        }

        private void toolStripButton2_Click(object sender, EventArgs e)
        {
            Query();
        }
    }
}