webapi中Route标签定义可选参数

Optional URI Parameters and Default Values

You can make a URI parameter optional by adding a question mark to the route parameter. If a route parameter is optional, you must define a default value for the method parameter.

public class BooksController : ApiController
{
    [Route("api/books/locale/{lcid:int?}")]
    public IEnumerable<Book> GetBooksByLocale(int lcid = 1033) { ... }
}

In this example, /api/books/locale/1033 and /api/books/locale return the same resource.

Alternatively, you can specify a default value inside the route template, as follows:

public class BooksController : ApiController
{
    [Route("api/books/locale/{lcid:int=1033}")]
    public IEnumerable<Book> GetBooksByLocale(int lcid) { ... }
}

This is almost the same as the previous example, but there is a slight difference of behavior when the default value is applied.

• In the first example ("{lcid?}"), the default value of 1033 is assigned directly to the method parameter, so the parameter will have this exact value.
• In the second example ("{lcid=1033}"), the default value of "1033" goes through the model-binding process. The default model-binder will convert "1033" to the numeric value 1033. However, you could plug in a custom model binder, which might do something different.

(In most cases, unless you have custom model binders in your pipeline, the two forms will be equivalent.)