在Web API中获取请求为null？

Question

I just started using web api and I was wondering if the parameter value is supposed to be null if you don't have any query parameters.

For example, I have this model:

[DataContract]
public class GetBooksRequest
{
    public int? BookLimit { get; set; }
}

Used in the following action

[HttpGet]
[Route("api/books")]
public IHttpActionResult Get([FromUri]GetBooksRequest request) {
  // request is null
}

Is parameter value supposed to be null if I hit api/books ?.

It hits my endpoint, but parameter is null . If I do api/books?booklimit=1 , then parameter is not null and the BookLimit property is set to 1 as expected.

I just wasn't sure if that's the way web api works.

Answer 1

Yes that is how it works. The framework inspects the request and will build up the model from the URI (because it was told to check by [FromUri] attribute) .

If it cannot build the model with the provided information the model/parameter will be set to its default value, in this case null . That is by design.

Source: Parameter Binding in ASP.NET Web API

Using [FromUri]

To force Web API to read a complex type from the URI, add the [FromUri] attribute to the parameter. The following example defines a GeoPoint type, along with a controller method that gets the GeoPoint from the URI.

 public class GeoPoint { public double Latitude { get; set; } public double Longitude { get; set; } } public ValuesController : ApiController { public HttpResponseMessage Get([FromUri] GeoPoint location) { ... } } 

The client can put the Latitude and Longitude values in the query string and Web API will use them to construct a GeoPoint. For example:

 http://localhost/api/values/?Latitude=47.678558&Longitude=-122.130989