When to use HttpResponseMessage and Request.CreateResponse

asp.net-web-api, c#

Solution

What is difference between HttpResponseMessage object and Request.CreateResponse(...) method?

It is probably obvious but `Request.CreateResponse` is a helper method for creating `HttpResponseMessage` object.

When we must use HttpResponseMessage object and When we must use Request.CreateResponse(...) method?

If you want to use the built-in content negotiation feature, use `Request.CreateResponse`. When you return an object, ASP.NET Web API has to serialize the object into response body. This could be generally JSON or XML (other media types are possible but you need to create the formatter). The media type chosen (JSON or XML) is based on the request content type, `Accept` header in the request and so on and content negotiation is the process that determines the media type to be used. By using `Request.CreateResponse`, you are automatically using the result of this process.

On the other hand, if you create `HttpResponseMessage` yourself, you have to specify a media formatter based on which the object will be serialized and by specifying the media formatter yourself, you can override the results of conneg.

EDIT Here is an example of how to specify JSON formatter.

public HttpResponseMessage Get(int id)
{
    var foo = new Foo() { Id = id };
    return new HttpResponseMessage()
    {
        Content = new ObjectContent<Foo>(foo,
                  Configuration.Formatters.JsonFormatter)
    };
}

With this, even if you send a request with `Accept:application/xml`, you will only get JSON.

Problem

When should we use the `HttpResponseMessage` object and when should we use the `Request.CreateResponse(...)` method? Also, what is the difference between the `HttpResponseMessage` object and the `Request.CreateResponse(...)` method?

Original source