Question

It compiles normal but when I try to iterate through result of the LINQ query I ‘ve got such exception The group by operation contains an expression that cannot be translated
The query is

var query0 = from c in dc.Prices
              where Convert.ToDateTime(c.data).CompareTo(left) >= 0
              && Convert.ToDateTime(c.data).CompareTo(right) <= 0
              && c.idsticker.Equals(x)
            group c by new { ((DateTime)c.data).Year, ((DateTime)c.data).Month }
                  into groupMonthAvg
                  select new
                  {
                      years = groupMonthAvg.Key.Year,
                      months = groupMonthAvg.Key.Month,
                      prices = groupMonthAvg.Average(i => i.value)
                  };

What expression in group by function is wrong?

Answer 1

Try this:

var query0 = from c in dc.Prices
             let date = Convert.ToDateTime(c.data)
             where date.CompareTo(left) >= 0 && date.CompareTo(right) <= 0 && c.idsticker.Equals(x)
             group c by new { date.Year, date.Month } into groupMonthAvg
             select new
             {
                 years = groupMonthAvg.Key.Year,
                 months = groupMonthAvg.Key.Month,
                 prices = groupMonthAvg.Average(i => i.value)
             };