没有找到NavigationLink工厂

我目前正在研究mvc4 web api odata服务，我想返回用户列表，其中用户有语言列表。当我想获得用户时，我得到以下错误:

错误:

<m:innererror>
<m:message>
The 'ObjectContent`1' type failed to serialize the response body for content type 'application/json; charset=utf-8'.
</m:message>
<m:type>System.InvalidOperationException</m:type>
<m:stacktrace/>
<m:internalexception>
<m:message>
No NavigationLink factory was found for the navigation property 'Languages' from entity type 'MvcWebRole1.Models.User' on entity set 'Users'. Try calling HasNavigationPropertyLink on the EntitySetConfiguration.
 Parameter name: navigationProperty
</m:message>
<m:type>System.ArgumentException</m:type>
<m:stacktrace>
at System.Web.Http.OData.Builder.EntitySetLinkBuilderAnnotation.BuildNavigationLink(EntityInstanceContext instanceContext, IEdmNavigationProperty navigationProperty, ODataMetadataLevel metadataLevel)
 at System.Web.Http.OData.Formatter.Serialization.ODataEntityTypeSerializer.WriteNavigationLinks(EntityInstanceContext context, ODataWriter writer, ODataSerializerContext writeContext)
 at System.Web.Http.OData.Formatter.Serialization.ODataEntityTypeSerializer.WriteEntry(Object graph, IEnumerable`1 propertyBag, ODataWriter writer, ODataSerializerContext writeContext)
 at System.Web.Http.OData.Formatter.Serialization.ODataEntityTypeSerializer.WriteObjectInline(Object graph, ODataWriter writer, ODataSerializerContext writeContext)
 at System.Web.Http.OData.Formatter.Serialization.ODataFeedSerializer.WriteFeed(Object graph, ODataWriter writer, ODataSerializerContext writeContext)
 at System.Web.Http.OData.Formatter.Serialization.ODataFeedSerializer.WriteObjectInline(Object graph, ODataWriter writer, ODataSerializerContext writeContext)
 at System.Web.Http.OData.Formatter.Serialization.ODataFeedSerializer.WriteObject(Object graph, ODataMessageWriter messageWriter, ODataSerializerContext writeContext)
 at System.Web.Http.OData.Formatter.ODataMediaTypeFormatter.<>c__DisplayClassa.<WriteToStreamAsync>b__9()
 at System.Threading.Tasks.TaskHelpers.RunSynchronously(Action action, CancellationToken token)
</m:stacktrace>
</m:internalexception>
</m:innererror>

我的用户是这样的:

public class User
{
    [Key]
    public int UserId { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string UserName { get; set; }
    public string Password { get; set; }
    public virtual ICollection<Language> Languages { get; set; }
    public User()
    {
        Languages = new List<Language>();
    }
}

和我的UsersController for OData看起来像这样:

public class UsersController : EntitySetController<User, int>
{
    WorldChatContext db = new WorldChatContext();
    public override IQueryable<User> Get()
    {
        return db.Users.AsQueryable();
    }
    protected override User GetEntityByKey(int key)
    {
        return db.Users.FirstOrDefault(p => p.UserId == key);
    }
    public override HttpResponseMessage Post(User entity)
    {
        db.Users.Add(entity);
        db.SaveChanges();
        return base.Post(entity);
    }
}

我正在调用我在路由中设置的以下url: http://127.0.0.1:81/odata/Users，如果我在用户模型中注释导航属性，它就会起作用。

我做错了什么?我已经尝试把[Serializable, KnownType(typeof(Language))]放在我的用户类之上，但由于某种原因我不能使用KnownType。我如何使我的OData工作与这个导航属性?

builder.EntitySet<Language>("languages");