Join Lambda Expression - linq

Question

im just trying to make a join from two entities.
the two entieties are as folows:
public partial class AnswerSet
{
public int Id { get; set; }
public string Ans { get; set; }
public bool IsTrue { get; set; }
public int QuestionId { get; set; }
public virtual QuestionSet QuestionSet { get; set; }
}
and
public partial class QuestionSet
{
public QuestionSet()
{
this.AnswerSets = new HashSet<AnswerSet>();
}
public int Id { get; set; }
public string Quest { get; set; }
public virtual ICollection<AnswerSet> AnswerSets { get; set; }
}
So, there are a question and an Answer Entity on the database. 1 Question has more answers (in my example 4). So now im tried this:
var v1 = db.QuestionSets
.Select(q => q)
.Where(q=> q.Id == 11)
.Join(db.AnswerSets,
q => q.Id,
a => a.QuestionId,
(a, q) => new { question = q });
So, now i have the following output when the expression is as above (see image 1):
Here i have just the Answers.
when i chage the expression to:
var v1 = db.QuestionSets
.Select(q => q)
.Where(q=> q.Id == 11)
.Join(db.AnswerSets,
q => q.Id,
a => a.QuestionId,
(q, a) => new { question = q });
then i have the following output (see image 2): (just the question, but 4 times. as many answers i have.)
So my question is, how can i join these two entities, that the Answers are a set in the QuestionSet entity?
thank you
Image 1
Image 2

Answer 1

You want a group join (see http://msdn.microsoft.com/en-us/library/bb311040.aspx)
var QAs =
from q in db.QuestionSets
join a in db.AnswerSets
on q.Id equals a.QuestionId into answers
select new { Question = q, Answers = answers };
In Extension Method syntax:
var QAs = db.QuestionSets
.GroupJoin(
db.AnswerSets,
q => q.Id,
a => a.QuestionId,
(q, answers) => new {Question = q, Answers = answers});
Hope that helps
PS. Use it like so:
foreach (var qa in QAs)
{
Console.WriteLine("Question #{0} has {1} answers",
qa.Question.Id, qa.Answers.Count());
}

Answer 2

What about leaving the Join technique for complex query and use Ef Eager Loading by using Include
var v1 = db.QuestionSets.Include(b = b.Answer);
or
var v1 = db.QuestionSets.Include("Answer");