Why my super simple ASP.NET Web API (mvc4)+Entity Framework 5 doesn't work?

Question

I spent days to know the problems of my work, but no luck.

1. I created new MVC4 Web API project.
2. Add EF5 with my database (Project>Add>ADO.NET Entity Da

Answer 1

As @danludwig comment, http://www.asp.net/web-api/overview/formats-and-model-binding/json-and-xml-serialization gives all answers about my problem.

Add below code in Global.asax solves the problem.

var json = GlobalConfiguration.Configuration.Formatters.JsonFormatter;
json.SerializerSettings.PreserveReferencesHandling = 
Newtonsoft.Json.PreserveReferencesHandling.All;