//实例化查询上下文

            using ( BookStoreEntities db = new  BookStoreEntities())

            {

                //找到需要价格和名称的数据实体对象

                var book = db.Books.FirstOrDefault(x => x.Title == "ASP.NET NVC 程序开发");

                if(book!=null)

                {

                    //更改属性值

                    book.Title = "ASP.NET NVC 程序开发";

                    book.Price = 30;

                    //保存更改,只有调用了SaveChannges()方法后,更新后的数据才能被写入数据库

                    db.SaveChanges();

                }

            }

            #region 使用事务新增

            using (BookStoreEntities db = new BookStoreEntities())

            {

                //声明事务对象

                System.Data.Common.DbTransaction tran = null;

                //手动打开链接并创建事务

                db.Conection.Open();

                tran = db.Connection.BeginTransaction();

                try

                {

                    var book = db.Books.FirstOrDefault(x => x.Title == "JavaScript语言与AJAX应用");

                    var order = new Orders() { Num = 1, Books = book, Address = "" };

                    db.AddToOrders(order);

                    db.SaveChanges();

                    order.Address = "中国湖北武汉";

                    db.SaveChanges();

                    //提交事务

                    tran.Commit();

                }

                //如果出现任何异常事务回滚

                catch (Exception)

                {

                    tran.Rollback();

                }

                finally

                {

                    //关闭连接

                    if (db != null && db.Connection.State != System.Data.ConnectionState.Closed)

                    {

                        db.Connection.Close();

                    }

                }

            #endregion