mainEntities2 dbcontext = new mainEntities2();
        private void btnAdd_Click(object sender, RoutedEventArgs e)
        {
            Students stu = new Students();
            stu.StudentName_ = "李四";
                      stu.StudentSex_ = "男";
                      stu.StudentAge_ = 19;
                      stu.StudentProvince_ = "上海";
                      stu.StudentPhone_ = "17468523001";
            dbcontext.Entry<Students>(stu).State = System.Data.Entity.EntityState.Added;
            int i = dbcontext.SaveChanges();
            string str = i == 1 ? "添加成功" : "添加失败";
            MessageBox.Show(str);
        }

        private void btnDel_Click(object sender, RoutedEventArgs e)
        {
            Students stu = new Students();
            stu.StudentNO_ = 1;
            dbcontext.Entry<Students>(stu).State = System.Data.Entity.EntityState.Deleted;
            int i = dbcontext.SaveChanges();
            string str = i == 1 ? "删除成功" : "删除失败";
            MessageBox.Show(str);
        }

        private void btnUpdate_Click(object sender, RoutedEventArgs e)
        {
            //修改整个
            //Students stu = new Students();
            //stu.StudentNO_ = 2;
            //stu.StudentName_ = "李四";
            //stu.StudentSex_ = "男";
            //stu.StudentAge_ = 19;
            //stu.StudentProvince_ = "上海";
            //stu.StudentPhone_ = "17468523001";
            //dbcontext.Entry<Students>(stu).State = System.Data.Entity.EntityState.Added;
            //int i = dbcontext.SaveChanges();
            //string str = i == 1 ? "修改成功" : "修改失败";
            //MessageBox.Show(str);


            //修改某个属性
            Students stu = new Students();
            stu.StudentNO_ = 2;
            stu.StudentName_ = "王霸26";
            dbcontext.Students.Attach(stu);//必须使用attach

            //dbcontext.Entry<Students>(stu).Property<string>(s => s.StudentName_).IsModified = true;
            dbcontext.Entry<Students>(stu).Property("StudentName_").IsModified = true;
            int i = dbcontext.SaveChanges();
            string str = i == 1 ? "修改成功" : "修改失败";
            MessageBox.Show(str);
        }

        private void btnSelect_Click(object sender, RoutedEventArgs e)
        {
            //便利所有
            foreach (var item in dbcontext.Students)
            {
                Console.WriteLine($"学号:{item.StudentNO_}   姓名:{item.StudentName_}");
            }


            //查询整个表女生的信息
            var temp = from s in dbcontext.Students where s.StudentSex_ == "女" select s;

            foreach (var item in temp)
            {
                Console.WriteLine($"学号:{item.StudentNO_}   姓名:{item.StudentName_}    性别:{item.StudentSex_}");
            }
            
        }