在linq的日期时间

Question

所以我试图从脚本任务中的表中获取最近的记录。该错误是在未来的LINQ查询，它看起来像：

"Could not Translate expression 'Table(SSASLogging).Select(r=>r.TimeStamp).Max()' into SQL and could not treat it as a local expression."

问题在于DateTime数据类型，但我需要的日期时间把它给我的SSIS变量。我知道这可以在一个执行SQL任务中轻松完成，但是我现在太放弃了！我知道有一些用于DateTime的LinqToSQL方法，但它们用于比较它看起来像，我不知道如何在这里应用它们。

public DateTime getLatest() 
    { 
     DateTime result = new DateTime(); 

     //temp dummy/defaul date is two days ago 
     result = DateTime.Now.AddDays(-2); 

     try 
     { 
      //get the data connection string from the connection manager 
      RW = (string)Dts.Connections["ReportingWarehouse"].ConnectionString; 

      //Remove the Provider, Auto Translate, and Application 
      //as it is not a parameter for the DataContext constructor 
      RW = RW.Remove(RW.IndexOf("Provider=SQLNCLI10.1;"), "Provider=SQLNCLI10.1;".Length); 
      RW = RW.Remove(RW.IndexOf("Auto Translate=False;"), "Provider=SQLNCLI10.1;".Length); 
      RW = RW.Remove(RW.IndexOf("Application"),RW.Length - RW.IndexOf("Application")); 



      MessageBox.Show(RW); 

      //get the last insertion date from the SSASLoging table 
      using (DataContext RWData = new DataContext(RW)) 
      { 
       Table<SSASLogging> records = RWData.GetTable<SSASLogging>(); 
       var rs = (from r in records 
         select r.TimeStamp).Max(); 
       //result = rs.FirstOrDefault(); 
      } 

     } 

     catch (Exception e) 
     { 
      MessageBox.Show("Exception in Retrieving latesttime" + e.Message + "/n" 
          + e.StackTrace); 
     } 

     return result; 
    } 

}//end partial class 


[Table] 
public class SSASLogging 
{ 
    [Column(Name = "CREATED_TIMESTAMP")] 
    private DateTime timeStamp; 

    public DateTime TimeStamp 
    { 
     get { return this.TimeStamp; } 
    } 
}//End SSASLogging 

Answer 1

尝试排序表和Take(1).ToList()。它应该返回List 0或1个元素。然后你可以使用FirstOrDefault，这将通过应用程序不受SQL执行，：

var rs = (from r in records 
      orderby r.TimeStamp descending 
      select r).Take(1).ToList().FirstOrDefault(); 

Answer 2

如果Max不工作，你看这个：

var maxDate = 
    (from r in records 
    orderby r.TimeStamp descending 
    select r.TimeStamp) 
    .FirstOrDefault(); 

Answer 3

您可以尝试排序依据

var rs = (from r in records orderby r.TimeStamp descending 
        select r).FirstOrDefault(); 

Answer 4

这可能是因为这一点：

http://msdn.microsoft.com/en-us/vstudio/ff963710.aspx

这样：

var rs = (from r in records.AsEnumerable() 
     select r.TimeStamp).Max(); 

或：

var rs = (from r in records 
     select r.TimeStamp).AsEnumerable().Max();