如何使用 linq 将多个表外部连接到实体

Question

我将 ASP.NET MVC 3 与 Entity Framework CodeFirst 一起使用

我有两个类如下：

问题：

public class Question
{
    public int ID { get; set; }
    public Target Target { get; set; }
    public string QuestionText { get; set; }
    public Category Category { get; set; }
    public QuestionType QuestionType { get; set; }
    public virtual ICollection<Answer> Answers { get; set; }
    public Unit Unit { get; set; }
}

答案：

public class Answer
{
    public int ID { get; set; }
    public virtual Question Question { get; set; }
    public string AnswerText { get; set; }
    public int Value { get; set; }
}

我也有这个 ViewModel：

public class QuestionViewModel
{
    public int ID { get; set; }
    public string Question { get; set; }
    public string QuestionType { get; set; }
    public string Target { get; set; }
    public string Category { get; set; }
    public string Unit { get; set; }
    public List<Answer> Answers { get; set; }
}

我想查询问题表并包含答案（如果有的话）。

我一直在尝试这种风格

        var question = (from q in hontgen.Questions
                        where q.ID == id
                        join qt in db.QuestionTypes on q.QuestionType equals qt
                        join t in db.Targets on q.Target equals t
                        join c in db.Categories on q.Category equals c
                        join u in db.Units on q.Unit equals u
                        join a in db.Answers on q.Answers equals a

                        select new QuestionViewModel() {
                            ID = q.ID,
                            Question = q.QuestionText,
                            QuestionType = qt.Type,
                            Category = c.CategoryName,
                            Unit = u.UnitName,
                            Target = t.TargetName,
                            Answers = a
                        }).Single();

但这当然不会滚动，因为 a 不是答案列表，而只是一个答案。

如何重写查询以获取集合中的所有答案，或“问题”中具有正确问题的所有答案，同时接受一个空的答案列表？

Answer 1

像下面这样的子查询呢

public class DataRepository
{
    public List<Question> Questions { get; set; }
    public IEnumerable<Answer> Answers { get; set; }

}


public class QandA
{

    DataRepository dr = new DataRepository();

    public void QueryQuestion(int id)
    {
        var question = (from q in dr.Questions
                        where q.ID == id

                        select new QuestionViewModel()
                        {
                            ID = q.ID,
                            Question = q.QuestionText,
                            Answers = (from a in dr.Answers 
                                        where a.Question == q
                                        select a)
                        });
    }

}

}