我有2张桌子。 MarkQuestion和问题。
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:
我尝试过这样的事情:
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 = ..
};
如何解决呢?
最佳答案
在我看来,您想要一个组联接,因此您有两个范围变量-一个代表一个问题,另一个代表该特定问题的所有已标记问题。
这是您要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,可以使用
GroupJoin
方法获得相同的结果。