如何將此SQL查詢轉換爲LINQ？

Question

我想下面的查詢LINQ轉換，

SELECT AVG(currentvalue) AS ChartAvg, 
     CONVERT(varchar(10), ReceivedDate, 103) AS RecDate 
    FROM DatapointValues 
    WHERE (CONVERT(varchar(10), ReceivedDate, 103) = '21/04/2011') 
GROUP BY CONVERT(varchar(10), ReceivedDate, 103) 

我用下面的LINQ，但沒有工作，

from datapointvalues in db.DatapointValues 
where 
Convert.ToString(datapointvalues.ReceivedDate) == "21/04/2011" 
group datapointvalues by new { 
Column1 = Convert.ToString(datapointvalues.ReceivedDate) 
} into g 
select new { 
    ChartAvg = (System.Decimal?)g.Average(p => p.currentvalue),  
    g.Key.Column1  
} 

Answer 1

看看這篇文章：http://msdn.microsoft.com/en-us/library/bb882657.aspx

var date = DateTime.Parse("21/04/2011"); 

var result = from datapointvalues in db.DatapointValues 
      where datapointvalues.ReceivedDate.Date.equals(date) 
      group datapointvalues by datapointvalues.ReceivedDate.Date 
      into g 
      select new 
      { 
       ChartAvg = g.Average(p => p.currentvalue), 
       RecDate = g.Key 
      };