LINQ连接查询中的列表

Question

我在使用LINQ时遇到了一个问题，我想知道在存储库中是否有一个快速的解决方案

GetCompletePackQuestion(int id)
    {
        var query = from q in DbSet where q.id == id
                    join a in DbContext.Set<answers>() on id equals a.question_id
                    join cc in DbContext.Set<correct_answers>() on id equals cc.question_id
                    select new CompletePackModel
                    {
                        Id = q.id,
                        Question = q.question,
                        CorrectAnswer = cc.answers.id,
                        Answers = q.answers.Select(ans => ans.answer)
                    };
        return query.SingleOrDefault();
    }

CompletePackModel的Answers属性是一个字符串列表。所以问题是:一个问题有很多答案，所以虽然q.id是一个int，问题字符串和answer_id一个单一的id(好吧，我应该采取连接到id表中的字符串)…最后一个答案应该是一个列表……

有办法解决这个问题吗?

感谢

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为什么它在查询中给我3个结果而不是一个?

Answer 1

我假设您正在使用实体框架(基于我看到的DbContext对象)。在这种情况下，你的Question类应该已经有了答案的集合。然后，您需要执行如下操作:

select new CompletePackModel
{
  Id = q.id,
  Question = q.question,                            
  CorrectAnswer = from answ in DbContext.Set<answers>() where answ.id == a.id select answ.answer,
  Answers = q.answers.Select(a => a.answer).ToList()
};

Answer 2

这样行吗?

var query = from q in DbContext.Set<questions>()
                join a in DbContext.Set<answers>() on q.id equals a.question_id
                join cc in DbContext.Set<correct_answers>() on q.id equals cc.question_id
                select new CompletePackModel
                {
                    Id = q.id,
                    Question = q.question,                            
                    CorrectAnswer = cc.answer,
                    Answers = DbContext.Set<answers>().Where(answ => answ.question_id == q.id).ToList()
                };