在Linq to Sql中使用记录的时间戳进行检测管理并发更新时的冲突
try{LinqToSqlDemoDataContext dataContext = new LinqToSqlDemoDataContext(); Order order1 = dataContext.Orders. Single (o = o.OrderID == 1 ); Order order2 = dataContext.Orders. Single (o = o.OrderID == 2 ); Order order3 = dataContext.Orders.
try
{
LinqToSqlDemoDataContext dataContext = new LinqToSqlDemoDataContext();
Order order1 = dataContext.Orders.Single(o => o.OrderID == 1);
Order order2 = dataContext.Orders.Single(o => o.OrderID == 2);
Order order3 = dataContext.Orders.Single(o => o.OrderID == 3);
Console.WriteLine('Order 1: ' + order1.Introduction);
Console.WriteLine('Order 2: ' + order2.Introduction);
Console.WriteLine('Order 3: ' + order3.Introduction);
Console.WriteLine();
order1.Introduction = 'Order 1 modified.';
order2.Introduction = 'Order 2 modified.';
order3.Introduction = 'Order 3 modified.';
dataContext.Log = Console.Out;
// 在下面的语句上设置一个断点
dataContext.SubmitChanges();
}
catch (ChangeConflictException e)
{
Console.WriteLine('---------- ' + e.Message + ' ----------');
}
LinqToSqlDemoDataContext db = new LinqToSqlDemoDataContext();
Order o1 = db.Orders.Single(o => o.OrderID == 1);
Order o2 = db.Orders.Single(o => o.OrderID == 2);
Order o3 = db.Orders.Single(o => o.OrderID == 3);
Console.WriteLine('Order 1: ' + o1.Introduction);
Console.WriteLine('Order 2: ' + o2.Introduction);
Console.WriteLine('Order 3: ' + o3.Introduction);
Console.ReadLine();
假设我们的数据表里有以下三条记录:
OrderID Name Introduction record_version
1 Order 1 This is order 1 <Binary data>
2 Order 2 This is order 2 <Binary data>
3 Order 3 This is order 3 <Binary data>
当程序进入到SubmitChanges语句的断点时,我们去
数据库中运行以下代码,以修改OrderID为2的记录。
UPDATE Order SET OrderID = "New Order 2" WHERE OrderID = 2
继续运行程序,最终控制台中会打印出以下信息:
Order 1: This is order 1
Order 2: This is order 2
Order 3: This is order 3
UPDATE [dbo].[Order]
SET [Introduction] = @p2
WHERE ([OrderID] = @p0) AND ([record_version] = @p1)
SELECT [t1].[record_version]
FROM [dbo].[Order] AS [t1]
WHERE ((@@ROWCOUNT) > 0) AND ([t1].[OrderID] = @p3)
-- @p0: Input Int (Size = 0; Prec = 0; Scale = 0) [1]
-- @p1: Input Timestamp (Size = 8; Prec = 0; Scale = 0) [SqlBinary(8)]
-- @p2: Input NVarChar (Size = 26; Prec = 0; Scale = 0) [Order 1 modified.]
-- @p3: Input Int (Size = 0; Prec = 0; Scale = 0) [1]
-- Context: SqlProvider(Sql2005) Model: AttributedMetaModel Build: 3.5.21022.8
UPDATE [dbo].[Order]
SET [Introduction] = @p2
WHERE ([OrderID] = @p0) AND ([record_version] = @p1)
SELECT [t1].[record_version]
FROM [dbo].[Order] AS [t1]
WHERE ((@@ROWCOUNT) > 0) AND ([t1].[OrderID] = @p3)
-- @p0: Input Int (Size = 0; Prec = 0; Scale = 0) [2]
-- @p1: Input Timestamp (Size = 8; Prec = 0; Scale = 0) [SqlBinary(8)]
-- @p2: Input NVarChar (Size = 26; Prec = 0; Scale = 0) [Order 2 modified.]
-- @p3: Input Int (Size = 0; Prec = 0; Scale = 0) [2]
-- Context: SqlProvider(Sql2005) Model: AttributedMetaModel Build: 3.5.21022.8
---------- 1 of 2 updates failed. ----------
Order 1: This is order 1
Order 2: This is order 2
Order 3: This is order 3
首先我们分别打印出三个Video对象的Introduction并将它们修改为新的值。在SubmitChanges方法调用之前,数据库中ID为2的记录已经被修改过了,因此在第一组UPDATE+SELECT调用成功之后——请注意,这是一次调用,Linq to Sql每次更新一条记录——在更新第二条记录之后发现了并发冲突。于是抛出异常(请注意异常的Message表示“两次更新其中有一次失败了”),第三条记录也不会再更新了。在冲突发生之后,ID为2和纪录自然没有被修改(WHERE条件不成立),但是第一条记录呢?从try...catch块之后的操作中看,ID为1的记录也没有被更新。
也就是说,第一次更新被回滚了。这自然是事务的作用。在调用(默认的) SubmitChanges方法时,Linq to Sql会把所有的更新放在同一个事务中,因此它们“共同进退”。但是由于业务
需求不同,有时候我们不希望某条记录的冲突导致了所有更新失败。自然, Linq to Sql也提供了这个方面的控制。在下一篇文章中,我们就来看一下Linq to Sql中与乐观并发控制有关的事务问题,以及出现并发冲突之后的解决方式。拼吾爱
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原文转自:http://www.ltesting.net