You want to GroupBy
the UserId, Date and presumably Deptname:
_context.Log.GroupBy(l => new { l.UserId, l.dates.Date, l.Deptname })
.Select(g => new { g.Key.UserId, g.Key.Date, g.Key.Deptname, Log = string.Join(",", g.Select(i => i.times)) });
Should select the first UserId
, Date
and Deptname
. Then join the log times together. Haven't checked this but seems like it should work.
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