在linq中分组和平均

Question

我有2张桌子.MarkQuestion和Question.

MarkQuestion has:
IDQuestion,
IDUser,
Mark

Question has:
IDQuestion,
Text

我想提取每个问题的文本和每个问题的平均分数:

我试过这样的事情:

var questions = from mark in Entities.MarkedQuestions
                          join question in Entities.Questions on mark.IDQuestion equals question.IDQuestion
                          group mark by mark.IDQuestion into markGroup,
                          question by question.IDQuestion into questionGroup
                          select new ModelView.MarkQuestionModel
                          {
                              AverageMark = markGroup.Average(x => x.Mark),
                              Text = ..
                          };

怎么解决这个？

Answer 1

听起来像你想要一个群组连接,所以你有两个范围变量 - 一个代表一个问题,另一个代表该特定问题的所有标记问题.

这是您使用的查询表达式语法:

var questions = from question in Entities.Questions
                join marked in Entities.MarkedQuestions
                    on question.IDQuestion equals marked.IDQuestion
                    into marks
                select new ModelView.MarkQuestionModel
                {
                    AverageMark = marks.Average(x => x.Mark),
                    Text = question.Text
                };

对于点表示法,您将使用该GroupJoin方法来获得相同的结果.