Parameters.Add和Parameters.AddWithValue的区别 [英] Difference between Parameters.Add and Parameters.AddWithValue

问题描述

我读了MSDN文档和示例<一个href=\"http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlcommand.parameters.aspx\">here我知道，对于一个 Paramters.Add 调用正确的语法是：

I read the MSDN documentation and examples here and I know that the correct syntax for a Paramters.Add call is :

   command.Parameters.Add("@ID", SqlDbType.Int);
   command.Parameters["@ID"].Value = customerID; 

您必须指定参数名称，在 SqlDbType ，以 .value的中的价值。

Where you have to specify the Parameter Name, the SqlDbType AND the Value with .Value.

现在的 Parameters.AddWithValue 调用正确的语法是：

Now the correct syntax for a Parameters.AddWithValue call is :

   command.Parameters.AddWithValue("@demographics", demoXml);

单行和跳过键入部分。

我的问题是：它是如何，当我像这样做，

My Question is : How is it that when I do it like this,

   command.Parameters.Add("@demographics", demoXml);
   // .Add method with .AddWithValue syntax

我没有得到任何错误编译，甚至怪异，执行code时，一切似乎都正常工作？

I don't get any compiling error and even weirder, everything seems to work properly when the code is executed ?

推荐答案

有是在功能方面没有区别。事实上，无论做到这一点：

There is no difference in terms of functionality. In fact, both do this:

return this.Add(new SqlParameter(parameterName, value));

他们去precated旧赞成的理由 AddWithValue 是添加额外的清晰度，以及因为第二个参数是对象，这使得它不会立即明显，有些人该添加正在调用，并且他们造成了很大的不同行为。

The reason they deprecated the old one in favor of AddWithValue is to add additional clarity, as well as because the second parameter is object, which makes it not immediately obvious to some people which overload of Add was being called, and they resulted in wildly different behavior.

在这个例子看看：

 SqlCommand command = new SqlCommand();
 command.Parameters.Add("@name", 0);

乍一看，它看起来像它调用添加（字符串名称，对象的值）过载，的但它不是的。它调用了添加（字符串名称，SqlDbType型）超载！这是因为0是隐式转换为枚举类型。因此，这两条线：

At first glance, it looks like it is calling the Add(string name, object value) overload, but it isn't. It's calling the Add(string name, SqlDbType type) overload! This is because 0 is implicitly convertible to enum types. So these two lines:

 command.Parameters.Add("@name", 0);

和

 command.Parameters.Add("@name", 1);

实际上导致被称为两种不同的方法。 1 不是转换为一个枚举含蓄，所以它选择了对象超载。随着 0 ，它选择的枚举超载。

Actually result in two different methods being called. 1 is not convertible to an enum implicitly, so it chooses the object overload. With 0, it chooses the enum overload.

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