Question

I tried to understand both and write sample code:

 public HttpResponseMessage Get()
 {
     var response = ControllerContext.Request
                         .CreateResponse(HttpStatusCode.BadRequest, "abc");

     throw new HttpResponseException(response);
 }

And:

 public HttpResponseMessage Get()
 {
     return ControllerContext.Request
                        .CreateResponse(HttpStatusCode.BadRequest, "abc");
 }

From Fiddle, I really didn’t see any differences between them, so what is the purpose of using HttpResponseException?

Answer 1

The main difference between the two is this. The exception is useful to immediately stop processing and exit. For example assume I have the following code

public class CustomerController : ApiController {
  private ICustomerContext repo;

  public CustomerController(ICustomerContext repo) {
    this.repo = repo;
  }

  public Customer Get(int id) {
    var customer = repo.Customers.SingleOrDefault(c=>c.CustomerID == id);
    if (customer == null) {
      throw new HttpResponseException(new HttpResponseMessage(HttpStatusCode.NotFound));
    }
    return customer;
  }
}

If this code runs and I pass an id that is not present, it will immediately stop processing and return a status code of 404.

If instead I return HttpResponseMessage, the request will happily continue the rest of its processing and return a 404. The main difference being end the request or not.

As Darrel said the exception is useful in cases where in some cases I want processing to continue (as in when customer is found) and in others I don’t.

The place where you might want to use something like HttpResponseMessage is in an Http POST to return a status code of 201 and set the location header. In that case I do want processing to continue. That would would do with this code.*

public class CustomerController : ApiController {
  private ICustomerContext repo;

  public CustomerController(ICustomerContext repo) {
    this.repo = repo;
  }

  public HttpResponseMessage Post(Customer customer) {
    repo.Add(customer);
    repo.SaveChanges();
    var response = Request.CreateResponse(HttpStatusCode.Created, customer);
    response.Headers.Location = new Uri(Request.RequestUri, string.format("customer/{0}", customer.id));
    return response;
  }
}

*note: If you are using the beta bits you would create a new HttpResponseMessage. I am using the later bits however which require you to use the CreateResponse extension method off of the Request.

Above, I am creating a response which sets the status code to 201, passes in the customer, and then sets the location header.

The response is then returned and the request continues processing.

Hope this helps