DbDataController content negotiation fails

Even if I askes specifically for xml, it keeps giving me back json:

public class DataServiceController : DbDataController<ListItCheckItContext> {

        public IQueryable<Category> GetCategories() {

            return DbContext.Categories.AsQueryable();
        }
    }

this is the request:

GET http://localhost:10914/api/DataService/GetItems

User-Agent: Fiddler
Accept: application/xml
Host: localhost:10914

And this is the response:

HTTP/1.1 200 OK
Cache-Control: no-cache
Pragma: no-cache
Transfer-Encoding: chunked
Content-Type: application/json; charset=utf-8
Expires: -1
Server: Microsoft-IIS/7.5
X-AspNet-Version: 4.0.30319
X-SourceFiles: =?UTF-8?B?RDpcRHJvcGJveFxBcHBzXEFTUE5FVE1WQ1NhbXBsZXNcc3JjXExpc3RJdENoZWNrSXRcTGlzdEl0Q2hlY2tJdFxhcGlcRGF0YVNlcnZpY2VcR2V0SXRlbXM=?=
X-Powered-By: ASP.NET
Date: Thu, 23 Feb 2012 21:06:29 GMT

65
[{"Category":null,"CategoryId":1,"CompletedOn":null,"Id":1,"IsCompleted":false,"Task":"Check this!"}]
0

Re: DbDataController content negotiation fails

tugberk_ugurlu_
tugberk_ugurlu_

Because the AbDataController override some of those feature. If you would return xml use APIController.

MVC DataController uses DataContractJsonSerilizer which requires models contain no Cycles

Re: DbDataController content negotiation fails

What does the Category type look like?

One possible explanation is that the XmlMediaTypeFormatter cannot serialize IQueryable<Category>.

By default, XmlMediaTypeFormatter uses XmlSerializer, but can be modified to use DataContractSerializer (config.Formatters.XmlFormatter.UseDataContractSerializer). Bing "XmlSerializer" for serialization issues to see if they sound familiar.

Alternatively, try using the DataContractSerializer as described above.

The content negotiation algorithm tries for a best match for both *type* and for required media type. If it fails matching the type, it will not use that MediaTypeFormatter, even if the media type matches. In your case, the JsonMediaTypeFormatter is probably saying "yes" to the Category type, and the XmlMediaTypeFormatter is probably saying "no". If only the type matches, that MediaTypeFormatter is used, regardless what you had in your Accept header.

Does that sound like a possibility for your object hierarchy?

Re: DbDataController content negotiation fails

Incidentally, I'm curious what others think of the content negotiation decision that "type is good enough if I can't match media type too".

Given your choice, what kind of response would you prefer to see?

BadRequest? It's really an issue with the types you are returning from the DbDataController/ApiController's actions.

InternalServerError? Those are always a joy to debug.

Incidentally, if you think returning a different media type based on a type-only match is unacceptable, you can replace the IFormatterSelector in the HttpConfiguration.ServiceResolver with one of your own. It can subclass the default FormatterSelector but 2nd guess the choice -- or throw an HttpResponseException with an HttpResponse of your choice.