Linq查询从三个表填充集合

Question

I have the following three tables:

[SURVEY_QUESTIONS]
(
[QuestionId]
[SurveyId],
[Question],
[AnswerType] 
)

[SURVEY_ANSWERS]
(
[AnswerId],
[QuestionId],
[ResponseId],
[Answer]
)

[SURVEY_RESPONSES]
(
[ResponseId],
[SurveyId]
)

I need to populate the following object and I have the ResponseId.

public class SurveyResponse
{
    public int ResponseId { get; set; }

    public string Question { get; set; }

    public string Answer { get; set; }
}

I started writing this method which would return a collection of the SurveyResponse object, but am not sure how to finish or what would be the best method to return my collection

    public static List<SurveyResponse> GetSurveyResponse(int responseId)
    {
        using (CaseDatabaseEntities entities = BaseDAL.GetNewEntities())
        {
            SURVEY_RESPONSES sr = entities.SURVEY_RESPONSES
                                                    .Where(r => r.ResponseId == responseId).FirstOrDefault();

            var Answers = entities.SURVEY_ANSWERS.Where(a => a.ResponseId == responseId);
            var Questions = entities.SURVEY_QUESTIONS.Where(q => q.SurveyId == sr.SurveyId);

            List<SurveyResponse> surveyResp = new List<SurveyResponse>();
            foreach (var q in Questions)
            {

            }

            return surveyResp;

        }
    }

Answer 1

I think this is what you are looking for.

public static List<SurveyResponse> GetSurveyResponse(int responseId)
{
    using (CaseDatabaseEntities entities = BaseDAL.GetNewEntities())
    {
        SURVEY_RESPONSES sr = entities.SURVEY_RESPONSES
                                                .Where(r => r.ResponseId == responseId).FirstOrDefault();

        var Answers = entities.SURVEY_ANSWERS.Where(a => a.ResponseId == responseId).;
        var Questions = entities.SURVEY_QUESTIONS.Where(q => q.SurveyId == sr.SurveyId);

        var questionsWithAnswers = (from q in Questions
                    join a in Answers on q.QuestionId equals a.QuestionId
                    select new SurveyResponse(){ ResponseId = a.responseId, Question = q.Question, Answer = a.Answer}).ToList()

        return questionsWithAnswers;

    }
}

I haven't tested the code.

Answer 2

This can best be done using joins in Linq. Assuming the column "ResponseId" in the answer table corresponds to the column "ResponseId" in the survey responses table you could do the following:

var responses = (from s in entities.SURVEY_RESPONSES 
                  join q in entities.SURVEY_QUESTIONS on s.SurveyId equals q.SurveyId
                  join a in entities.SURVEY_ANSWERS on s.ResponseId equals a.ResponseId
                  where s.ResponseId == responseId
                  select new {s.ResponseId, q.Question, a.Answer});

List<SurveyResponse> surveyResp = new List<SurveyResponse>();
foreach (var r in responses)
{
  SurveyResponse survey = new SurveyResponse();
  survey.ResponseId = r.ResponseId;
  survey.Question = r.Question;
  survey.Answer = r.Answer;
  surveyResp.Add(survey);
}

return surveyResp;