Linq FirstOrDefault返回多个

Question

I am having a strange issue in which a linq statement is returning multiple entities even though it has .FirstOrDefault() .

var endlog = from e in endLogs
             where e.user_id == log.user_id && e.end_time <= log.start_time
             group e by e.end_time into g
             select g.OrderByDescending(x => x.end_time).FirstOrDefault();

user_state_log eLog = endlog.SingleOrDefault();

What this is doing is selecting the log with the most recent end time compared to the supplied log . I get an exception on user_state_log eLog = endlog.SingleOrDefault() stating that there is more than one entity in the variable. Any ideas?

Answer 1

Are you sure you mean to use group e by instead of orderby ? There is a chance that the grouping will contain multiple entities.

Answer 2

Your FirstOrDefault is applying to the result of select , which occurs once for every group ( g ). I believe the result is every value in endlog will be a single item rather than a group.

You might have intended for the FirstOrDefault to apply to the query rather than the projection ( select ):

var endlog = (from e in endLogs
             where e.user_id == log.user_id && e.end_time <= log.start_time
             group e by e.end_time into g
             select g.OrderByDescending(x => x.end_time)).FirstOrDefault();