The Constraint Entry 'httpMethod' on the Route Must Have a String Value

问题

I have an asp.net Web API project, and in my WebApiConfig file, I have the following route defined:

config.Routes.MapHttpRoute(
    name: "Web API Get",
    routeTemplate: "api/{controller}",
    defaults: new { action = "Get" },
    constraints: new { httpMethod = new HttpMethodConstraint("GET") }
    );

For integration testing purposes, I want to make a request to an HttpSelfHostServer to verify that we are receiving the proper data back from the api call. I am making the HttpRequestMessage as follows:

var httpMethod = new HttpMethod("GET");
var request = new HttpRequestMessage(httpMethod, "http://localhost:XXXX/api/User/");
var results = _client.SendAsync(request).Result;

I would expect that this would call the Get method on the UserController and then return the results as defined in that method. However, I instead get the following exception:

System.InvalidOperationException: The constraint entry 'httpMethod' on the route with route template 'api/{controller}' must have a string value or be of a type which implements 'IHttpRouteConstraint'

This same url (http://localhost:XXXX/api/User/) works without error when I use it in the browser, so I am pretty sure the issue has to be in the way I am sending the request to the HttpSelfHostServer through the HttpClient. I have tried using the HttpMethod.Get constant instead, but that also threw the same error.

Does anyone have any idea how I could resolve this issue?

回答1:

Make sure that you are using the proper type for your constraint:

constraints: new { httpMethod = new System.Web.Http.Routing.HttpMethodConstraint(HttpMethod.Get) }

I guess you were using System.Web.Routing.HttpMethodConstraint which is an entirely different class used for ASP.NET MVC routing and which has nothing to do with ASP.NET Web API routing.

来源：https://stackoverflow.com/questions/18404226/the-constraint-entry-httpmethod-on-the-route-must-have-a-string-value