| 当与数据库交互时首先应该创建连接。此连接告诉其余的ADO.NET代码：它将与哪个数据库打交道。它管理所有与特定数据库协议有关联的低级逻辑。这种方式使与数据库连接十分简单，你需要写的代码只是实体化connection对象，打开connection，在完事之后关闭connection。因为ADO.NET以这种方式构造其它的类，某些时候你甚至不需要做太多的工作。
Although working with connections is very easy in ADO.NET, you need to understand connections in order to make the right decisions when coding your data access routines. Understand that a connection is a valuable resource. Sure, if you have a stand-alone client application that works on a single data base one one machine, you probably don''''t care about this. However, think about an enterprise application where hundreds of users throughout a company are accessing the same data base. Each connection represents overhead and there can only be a finite amount of them. To look at a more extreme case, consider a Web site that is being hit with hundreds of thousands of hits a day. Applications that grab connections and don''''t let them go can have seriously negative impacts on performance and scalability.
尽管在ADO.NET中使用连接非常简单，你需要理解连接以便在数据存取规则中采用正确的策略。理解连接是非常有价值的。当然，如果在一台机器上有一个单独的客户端应用程序使用单独的数据库，你可能不用关心这个。然而，考虑一个企业级应用程序，全公司的大量用户都存取同样的数据库。每一次连接都代表损耗并且连接的数量都是有限的。再来看一个更加极端的情况，考虑web站点每天要承受成千上万的访问。应用程序保持连接而不让它们断开会对性能和可测量性带来严重的负面影响。
Creating a SqlConnection Object
创建SqlConnection对象
A SqlConnection is an object, just like any other C# object. Most of the time, you just declare and instantiate the SqlConnection all at the same time, as shown below:
SqlConnection是对象，就像C#中其它的对象一样。很多时候，你只需要声明并实例化SqlConnection，如下所示：
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