How to throw exception in Web API?

Question

How can I throw a exception to in ASP.net Web Api?

Below is my code:

public Test GetTestId(string id)
{
    Test test = _test.GetTest(id);

    if (test == null)
    {
        throw new HttpResponseException(HttpStatusCode.NotFound);
    }

    return test;
}

I don't think I am doing the right thing, How do my client know it is a HTTP 404 error?

Answer 1

It's absolutely fine.

Alternatively, if you wish to provide more info (to allow, as you say, the client to distinguish from regular 404):

    if (test == null)
    {
         throw new HttpResponseException(Request.CreateErrorResponse(HttpStatusCode.NotFound, 
"this item does not exist"));
    }

Answer 2

This blogpost should help you understand WebAPI error handling a bit better.

What you have in your code snippet should work. The server will send back a 404 Not Found to the client if test is null with no response body. If you want a response body, you should consider using Request.CreateErrorResponse as explained in the blog post above and passing that response to the HttpResponseException.