ef-code-first – 在WebAPI Controller中序列化EF Code First 5.

You must write an attribute 'type'='object' after writing the attribute 
with local name '__type'.

这是我正在做的返回数据：

var everything = dc.Categories
            .Include(c => c.Products);

我的类定义相当简单：

public class Category
{
    public int CategoryId { get; set; }
    public string Title { get; set; }

    public virtual ICollection<Product> Products { get; set; }
}

public class Product
{
    public int ProductId { get; set; }
    public string Title { get; set; }

    public virtual Category Category { get; set; }
}

public class ProductDataContext : DbContext
{
    public DbSet<Category> Categories { get; set; }
    public DbSet<Product> Products { get; set; }
}

我也尝试删除’虚拟’,但后来我得到循环引用.我尝试将ICollection产品上的setter设置为私有(如此处建议：http://forums.asp.net/t/1773164.aspx/1),这样可以清除错误,但之后我的产品不是返回的JSON的一部分.

我需要做些什么来使数据与类别及其产品序列化？

编辑
这是我得到的堆栈跟踪：

[SerializationException: Object graph for type 'System.Collections.Generic.List`1[[Test.Models.Product,Test.Models,Version=1.0.0.0,Culture=neutral,PublicKeyToken=null]]' contains cycles and cannot be serialized if reference tracking is disabled.]
System.Web.Http.WebHost.HttpControllerHandler.EndProcessRequest(IAsyncResult result) +30206
System.Web.Http.WebHost.HttpControllerHandler.System.Web.IHttpAsyncHandler.EndProcessRequest(IAsyncResult result) +10
System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +9478661
System.Web.HttpApplication.ExecuteStep(IExecutionStep step,Boolean& completedSynchronously) +178