Linq to Sql学习总结5

修改并发异常ChangeConfictException//测试修改并发异常ChangeConfictExceptionvar query = from p in ctx.Productswhere p.CategoryID == 1select p;foreach (var p in query){p.UnitsInStock = Convert.ToInt16(p....

修改并发异常ChangeConfictException

//测试修改并发异常ChangeConfictException
            var query = from p in ctx.Products
                        where p.CategoryID == 1
                        select p;
            foreach (var p in query)
            {
                p.UnitsInStock = Convert.ToInt16(p.UnitsInStock - 1);
            }
            ctx.SubmitChanges();// 在这里设断点,程序运行到此处时，在数据库执行如下T_SQL操作
            /* UPDATE dbo.Products SET UnitsInStock = UnitsInStock - 2 WHERE CategoryID=1 */
            //然后继续运行程序，会抛出修改并发异常ChangeConfictException
            /* 原因分析：当客户端提交的修改对象自读取之后已经在数据库中发生改动，就产生了修改并发。*/
            /* 不考虑并发修改异常设置：实体类属性column特性增加UpdateCheck = UpdateCheck.Never
             * 不考虑并发修改异常情况下，默认是最后一次更新起作用 */

处理修改并发异常ChangeConfictException

//处理修改并发异常ChangeConfictException
            var query = from p in ctx.Products
                        where p.ProductID == 1
                        select p;
            foreach (var p in query)
            {
                p.UnitsInStock = Convert.ToInt16(p.UnitsInStock - 1);
            }
            try
            {
                ctx.SubmitChanges(ConflictMode.ContinueOnConflict);
            }
            catch (ChangeConflictException)
            {
                foreach (ObjectChangeConflict cc in ctx.ChangeConflicts)
                {
                    Products product = (Products)cc.Object;
                    cc.Resolve(RefreshMode.OverwriteCurrentValues);// 放弃当前进程更新，所有更新以原先其它进程更新为准
                    //cc.Resolve(RefreshMode.KeepCurrentValues); // 放弃原先其它进程更新，所有更新以当前进程更新为准
                    //cc.Resolve(RefreshMode.KeepChanges); // 原先其它进程更新有效，冲突字段以当前进程更新为准
                }
            }

            ctx.SubmitChanges();

//针对不同策略处理不同字段修改并发异常ChangeConfictException
            var query = from p in ctx.Products
                        where p.ProductID == 1
                        select p;
            foreach (var p in query)
            {
                p.UnitsInStock = Convert.ToInt16(p.UnitsInStock - 1);
            }
            try
            {
                ctx.SubmitChanges(ConflictMode.ContinueOnConflict);
            }
            catch (ChangeConflictException)
            {
                //遍历并发冲突对象集合
                foreach (ObjectChangeConflict cc in ctx.ChangeConflicts)
                { 
                    //遍历当前冲突对象更新失败的成员（即更新失败的列）
                    foreach (MemberChangeConflict mc in cc.MemberConflicts)
                    {
                        if (mc.Member.Name == "UnitsInStock")
                        {
                            mc.Resolve(RefreshMode.KeepCurrentValues); // 放弃原先其它进程更新，所有更新以当前进程更新为准
                        }
                        else if (mc.Member.Name == "UnitPrice")
                        {
                            mc.Resolve(RefreshMode.OverwriteCurrentValues); // 放弃当前进程更新，所有更新以原先其它进程更新为准
                        }
                        else
                        {
                            mc.Resolve(RefreshMode.KeepChanges); // 原先其它进程更新有效，冲突字段以当前进程更新为准
                        }
                    }
                }
            }

            ctx.SubmitChanges();

事务：

//Linq to sql在提交更新的时候默认会创建事务，一部分修改发生错误的话其它修改也不会生效：
            //假设数据库中已经存在顾客ID为“ALFKI”的记录，那么第二次插入操作失败将会导致第一次的插入操作失效。
            ctx.Customers.InsertOnSubmit(new Customers { CustomerID = "abcdf", CompanyName = "zhuye" });
            ctx.Customers.InsertOnSubmit(new Customers { CustomerID = "ALFKI", CompanyName = "zhuye" });
            ctx.SubmitChanges();

使用事务

            ctx.Connection.Open();
            ctx.Transaction = ctx.Connection.BeginTransaction();
            ctx.Customers.InsertOnSubmit(new Customers { CustomerID = "abcdf", CompanyName = "zhuye" });
            ctx.Customers.InsertOnSubmit(new Customers { CustomerID = "ALFKI", CompanyName = "zhuye" });
            try
            {
                ctx.SubmitChanges();
                ctx.Transaction.Commit();
            }
            catch
            {
                ctx.Transaction.Rollback();
            }
            ctx.Connection.Close();

使用TransactionScope

            using (TransactionScope tranScope = new TransactionScope())
            {
                ctx.Customers.InsertOnSubmit(new Customers { CustomerID = "abcdf", CompanyName = "zhuye" });
                ctx.Customers.InsertOnSubmit(new Customers { CustomerID = "ALFKI", CompanyName = "zhuye" });
                tranScope.Complete();
            }