EF 增删改查

using (var dc = new SchoolContext())
            {
                ////GRADE g = new GRADE() { GradeId=2 };
                //var greadeinfo = dc.Grades.Find(2);
                //STUDENT stu = new STUDENT() { STUDENTID = 3, STUDENTNAME = "李四", HEIGHT = 180.5F, WEIGHT = 140.5F, DATEOFBIRTH = DateTime.Now, PHOTO = "987654321", GRADE= greadeinfo };

                ////dc.Grades.Add(g);
                //dc.Students.Add(stu);
                //dc.SaveChanges();
                // 查询内容
                //IQueryable<STUDENT> stu = dc.Students;
                //foreach (var item in stu)
                //{
                //    MessageBox.Show(item.STUDENTID+"   "+item.STUDENTNAME);
                //}
                //如果查询内容为空
                //var stu=dc.Students.Where(t => t.STUDENTID == 5).FirstOrDefault();
                //if(stu!=null)
                //{
                //    MessageBox.Show(stu.STUDENTID + "   " + stu.STUDENTNAME);
                //}
                //排序
                //IQueryable<STUDENT> stu = dc.Students.OrderBy(t => t.STUDENTID).ThenBy(t => t.GRADE);
                //foreach (var item in stu)
                //{
                //    MessageBox.Show(item.STUDENTID + "   " + item.STUDENTNAME);
                //}

                //修改方法1
                //var stu = dc.Students.Find(1);
                //if(stu!=null)
                //{
                //    stu.STUDENTNAME = "小张";
                //}
                //dc.SaveChanges();

                //修改方法2 通过自己创建的对象
                //STUDENT stu = new STUDENT() { STUDENTID=3, STUDENTNAME="小三" };// 将对象加入EF容器，并获取当前实体对象的状态管理对象
                //DbEntityEntry<STUDENT> s=dc.Entry<STUDENT>(stu);
                //s.State = System.Data.Entity.EntityState.Unchanged;
                //s.Property("STUDENTNAME").IsModified=true;

                //dc.SaveChanges();

                //修改方法3  与 方法2 作用一样
                STUDENT stu = new STUDENT() { STUDENTID = 2, STUDENTNAME = "小三1" };
                var s = dc.Students.Attach(stu);
                s.STUDENTNAME = "小er";
                dc.SaveChanges();

                //删除内容
                //STUDENT stu = new STUDENT() { STUDENTID = 3, STUDENTNAME = "小三1" };
                //dc.Students.Attach(stu);
                //dc.Students.Remove(stu);
                //dc.SaveChanges();

                //MessageBox.Show("创建成功");
            }