CODEWITHSUNDEEP
asp.net-web-api2asp.net-web-api-routing
Stuart Hemming
Stuart Hemming

Reputation: 1663

UrlHelper.Link() returns null

I know that there are a number of questions here that have this title, but, having been through them, I do not believe any of the posted solutions help.

I have the following code in a Web Api v2.1 Controller...

    [VersionedRoute("{id:int}", 1, Name="GetEvent")]
    [HttpGet]
    public IHttpActionResult Get(int id)
    {
        try
        {
            var helper = new UrlHelper(Request);
            var link = helper.Link("GetEvent", new { id = id });
            var result = ApiBL.V1Get(id);
            if (result == null)
            {
                return NotFound();
            }
            return Ok(result);
        }
        catch (Exception ex)
        {
            throw new ApiHttpResponseException(HttpStatusCode.BadRequest, ex);
        }
    }

Putting a breakpoint on the line after the line on which link is assigned, I can see that it is null. I can also see that Request has what I'd expect to see...

{Method: GET, RequestUri: 'http://localhost:8087/atlas/api/events/50', Version: 1.1, Content: System.Net.Http.StreamContent, Headers:
{
  Authorization: Basic blahblahblah
  Host: localhost:8087
  Content-Length: 31
  Content-Type: application/json
}}

And that helper is non-null.

Below is the definition of the VersionedRouteAttribute class

public class VersionedRouteAttribute : RouteFactoryAttribute
{
    public VersionedRouteAttribute(string template, int allowedVersion)
        : base(template)
    {
        AllowedVersion = allowedVersion;
    }

    public int AllowedVersion { get; private set; }

    public override IDictionary<string, object> Constraints
    {
        get
        {
            var constraints = new HttpRouteValueDictionary();
            constraints.Add("version", new VersionConstraint(AllowedVersion));
            return constraints;
        }
    }
}

I believe, from everything I've read, that this should work. I simply can't figure out what's wrong. I'd appreciate any pointers.

Upvotes: 2

Views: 2978

Answers (1)

Kiran
Kiran

Reputation: 57939

I believe you are using the RoutingConstraintsSample from here which demonstrates versioning with attribute routing...if yes, then the VersionConstraint in that sample has a bug...you can modify the Match method of that to like below:

public bool Match(HttpRequestMessage request, IHttpRoute route, string parameterName, IDictionary<string, object> values, HttpRouteDirection routeDirection)
{
    if (routeDirection == HttpRouteDirection.UriResolution)
    {
        int version = GetVersionHeader(request) ?? DefaultVersion;

        return (version == AllowedVersion);
    }

    return true; 
}

Also why are you instantiating UrlHelper yourself as its already provided to you by the Url property that is available on the controller.

Upvotes: 3

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