DomainContext, Silverlight 3, code behind, Edit EntitySet

I'm trying to get my brain wraped around Silverlight RIA

I'm to a point where I can create an object with a collection of objects which also has a collection of objects.

Test object that holds test questions, that holds question answers.

I have the associations set up and the the data makes it to to silverlight app.

So in my loaded callback....i can see all the data in up

   private void TestLoaded(LoadOperation lo)
    {
            var ce =dc.Tests.CanEdit;
            dc.Tests.ToList()[0].TestQuestions.ToList()[0].StudentAnswerID = 2;
    }

var ce =dc.Tests.CanEdit; //CanEdit = true

but the next line gives the error: This EntitySet of type 'SilverlightApplication2.Web.Question' does not support the 'Edit' operation.

So my question is why does CanEdit = true? And what is a more graceful way of setting the value in code behind?

rest of the code.....

        public class Test
    {
        private List<Question> _testQuestions = new List<Question>();

        [Key]
        public int TestID { get; set; }

        public string TestName { get; set; }


        [Include]
        [Association("Assoc1", "TestID", "TestID,QuestionID")]
        public List<Question> TestQuestions
        {
            get { return _testQuestions; }
            set { _testQuestions = value; }
        }
    }


    public class Question
    {
        private List<Answer> _questionAnswers = new List<Answer>();

        [Key]
        public int TestID { get; set; }

        [Key]
        public int QuestionID { get; set; }

        public string QuestionText { get; set; }

        public int CorrectAnswerID { get; set; }
        public int StudentAnswerID { get; set; }

        [Include]
        [Association("Assoc2", "QuestionID", "QuestionID,AnswerID")]
        public List<Answer> QuestionAnswers
        {
            get { return _questionAnswers; }
            set { _questionAnswers = value; }
        }
    }



    public class Answer
    {
        [Key]
        public int QuestionID { get; set; }

        [Key]
        public int AnswerID { get; set; }

        public string AnswerText { get; set; }
    }

//data populator

 public class TestBuilder
{

    public List<Test> MakeATest()
    {
        var ret = new List<Test>();

        var t = new Test()
        {
            TestID = 1,
            TestName = "The Test",
        };

        var tq = new Question() { TestID = 1, QuestionID = 1, CorrectAnswerID=1,  QuestionText = "T1Q1" };

        var a = new Answer() { QuestionID = 1, AnswerID = 1, AnswerText = "T1Q1A1" };
        tq.QuestionAnswers.Add(a);

        a = new Answer() { QuestionID = 1, AnswerID = 2, AnswerText = "T1Q1A2" };
        tq.QuestionAnswers.Add(a);

        a = new Answer() { QuestionID = 1, AnswerID = 3, AnswerText = "T1Q1A3" };
        tq.QuestionAnswers.Add(a);

        a = new Answer() { QuestionID = 1, AnswerID = 4, AnswerText = "T1Q1A4" };
        tq.QuestionAnswers.Add(a);
        t.TestQuestions.Add(tq);


        //second question
        tq = new Question() { TestID = 1, QuestionID = 2, CorrectAnswerID = 3, QuestionText = "T1Q2" };

        a = new Answer() { QuestionID = 2, AnswerID = 1, AnswerText = "T1Q2A1" };
        tq.QuestionAnswers.Add(a);

        a = new Answer() { QuestionID = 2, AnswerID = 2, AnswerText = "T1Q2A2" };
        tq.QuestionAnswers.Add(a);

        a = new Answer() { QuestionID = 2, AnswerID = 3, AnswerText = "T1Q2A3" };
        tq.QuestionAnswers.Add(a);

        a = new Answer() { QuestionID = 2, AnswerID = 4, AnswerText = "T1Q2A4" };
        tq.QuestionAnswers.Add(a);
        t.TestQuestions.Add(tq);


        //third question
        tq = new Question() { TestID = 1, QuestionID =3, CorrectAnswerID = 4, QuestionText = "T1Q3" };

        a = new Answer() { QuestionID = 3, AnswerID = 1, AnswerText = "T1Q3A1" };
        tq.QuestionAnswers.Add(a);

        a = new Answer() { QuestionID = 3, AnswerID = 2, AnswerText = "T1Q3A2" };
        tq.QuestionAnswers.Add(a);

        a = new Answer() { QuestionID = 3, AnswerID = 3, AnswerText = "T1Q3A3" };
        tq.QuestionAnswers.Add(a);

        a = new Answer() { QuestionID = 3, AnswerID = 4, AnswerText = "T1Q3A4" };
        tq.QuestionAnswers.Add(a);
        t.TestQuestions.Add(tq);

        ret.Add(t);

        return ret;
    }
}

Domain Service.....

 [EnableClientAccess()]
public class TestDomainService : DomainService
{
    public IEnumerable<Test> GetTest()
    {
        var tb = new TestBuilder();
        return tb.MakeATest();
    }

    public void InsertTest(Test currentData)
    {}

    public void UpdateTest(Test currentData)
    {}

    public void DeleteTest(Test currentData)
    {}
}

Silverlight side......

      private void GetTest_Click(object sender, RoutedEventArgs e)
    {
        dc.Load(dc.GetTestQuery(),
                LoadBehavior.RefreshCurrent ,
                TestLoaded,
                null);
    }


    private void TestLoaded(LoadOperation lo)
    {
            var ce =dc.Tests.CanEdit;
            dc.Tests.ToList()[0].TestQuestions.ToList()[0].StudentAnswerID = 2;
    }

Why are you calling ToList()? RIA returns an EntitySet which inherits from IEnumerable so you shouldnt need to put it in a list. I would suggest trying a linq statement like:

using System.Linq;
Test mytest = dc.Tests.Where( x=> x.StudentAnswerID = 2).FirstorDefault();

As to the editing problem... If you are using Entity Framework as your data model be sure to check the checkbox "enable editing" when you create your domain service. CanEdit is a readonly value that tells you whether or not editing is allowed.