Substract 2 datatables using linq

Question

我想使用唯一列值减去2个数据表的列值并分配新的结果数据表。

public void getAllTopActivityData() 
    { 
     dtTopAllTemp.Clear(); 
     odagetTopAllTemp = new OracleDataAdapter(getTopAll, oradb); 
     odagetTopAllTemp.Fill(dtTopAllTemp); 

     if (isFirst == false) 
     { 
      isFirst = true; 
      dtTopAllTempOld = dtTopAllTemp;   
     } 

     var result = (from dr1 in dtTopAllTempOld.AsEnumerable() 
         from dr2 in dtTopAllTemp.AsEnumerable() 
         where dr1.Field<string>("EVENT") == dr2.Field<string>("EVENT") 
         select new 
         { 
          SAMPLE_TIME = dr1.Field<DateTime>("SAMPLE_TIME"), 
          INST_ID = dr1.Field<int>("INST_ID"), 
          WAIT_CLASS = dr1.Field<string>("WAIT_CLASS"), 
          EVENT = dr1.Field<string>("EVENT"), 
          WAITS = ((dr2["WAITS"] == DBNull.Value ? 0 : dr2.Field<double>("WAITS")) - (dr1["WAITS"] == DBNull.Value ? 0 : dr1.Field<double>("WAITS"))) 
      }).ToList(); 

    ultraGrid1.DataSource = result;/This doesn't work. 
    -- ultraGrid1.DataSource = dtTopAllTemp;/This brings data. 
    -- ultraGrid1.DataSource = dtTopAllTempOld;/This brings data. All it works. 


     dtTopAllTempOld = dtTopAllTemp; 
    } 

但是，我收到了'Invalid Cast Exception'错误。我再次检查了所有列数据类型是否正常。

konum: System.Data.DataRowExtensions.Field[T](DataRow row, String columnName) 
    konum: Oratify.Main.<getAllTopActivityData>b__188_3(<>f__AnonymousType0`2 <>h__TransparentIdentifier0) C:\Users\sezer\Desktop\AllC\Oratify\Oratify\Oratify\Main.cs içinde: satır 1495 
    konum: System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext() 
    konum: System.Collections.Generic.List`1..ctor(IEnumerable`1 collection) 
    konum: System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source) 
    konum: Oratify.Main.getAllTopActivityData() C:\Users\sezer\Desktop\AllC\Oratify\Oratify\Oratify\Main.cs içinde: satır 1492 
    konum: Oratify.Main.timer_TimerTopSQL(Object sender, EventArgs e) C:\Users\sezer\Desktop\AllC\Oratify\Oratify\Oratify\Main.cs içinde: satır 1534 
    konum: System.Windows.Forms.Timer.OnTick(EventArgs e) 
    konum: System.Windows.Forms.Timer.TimerNativeWindow.WndProc(Message& m) 
    konum: System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam) 
    konum: System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg) 
    konum: System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData) 
    konum: System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context) 
    konum: System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context) 
    konum: System.Windows.Forms.Application.Run(Form mainForm) 
    konum: Oratify.Program.Main() C:\Users\sezer\Desktop\AllC\Oratify\Oratify\Oratify\Program.cs içinde: satır 19</StackTrace><ExceptionString>System.InvalidCastException: Belirtilen atama geçerli değil. 
    konum: System.Data.DataRowExtensions.UnboxT`1.ValueField(Object value) 
    konum: System.Data.DataRowExtensions.Field[T](DataRow row, String columnName) 
    konum: Oratify.Main.&amp;lt;getAllTopActivityData&amp;gt;b__188_3(&amp;lt;&amp;gt;f__AnonymousType0`2 &amp;lt;&amp;gt;h__TransparentIdentifier0) C:\Users\sezer\Desktop\AllC\Oratify\Oratify\Oratify\Main.cs içinde: satır 1495 
    konum: System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext() 
    konum: System.Collections.Generic.List`1..ctor(IEnumerable`1 collection) 
    konum: System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source) 
    konum: Oratify.Main.getAllTopActivityData() C:\Users\sezer\Desktop\AllC\Oratify\Oratify\Oratify\Main.cs içinde: satır 1492 
    konum: Oratify.Main.timer_TimerTopSQL(Object sender, EventArgs e) C:\Users\sezer\Desktop\AllC\Oratify\Oratify\Oratify\Main.cs içinde: satır 1534 
    konum: System.Windows.Forms.Timer.OnTick(EventArgs e) 
    konum: System.Windows.Forms.Timer.TimerNativeWindow.WndProc(Message&amp;amp; m) 
    konum: System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam) 
    konum: System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG&amp;amp; msg) 
    konum: System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData) 
    konum: System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context) 
    konum: System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context) 
    konum: System.Windows.Forms.Application.Run(Form mainForm) 
    konum: Oratify.Program.Main() C:\Users\sezer\Desktop\AllC\Oratify\Oratify\Oratify\Program.cs içinde: satır 19</ExceptionString></Exception></TraceRecord> 

Answer 1

public partial class DTLinq : Form 
    { 
     DataTable dtTopAllTempOld = new DataTable(); 
     DataTable dtTopAllTemp = new DataTable(); 

     public DTLinq() 
     { 
      InitializeComponent(); 
     } 

     private void DTLinq_Load(object sender, EventArgs e) 
     { 
      dtTopAllTempOld.Columns.Add("SAMPLE_TIME", typeof(DateTime)); 
      dtTopAllTempOld.Columns.Add("INST_ID", typeof(int)); 
      dtTopAllTempOld.Columns.Add("WAIT_CLASS", typeof(string)); 
      dtTopAllTempOld.Columns.Add("EVENT", typeof(string)); 
      dtTopAllTempOld.Columns.Add("WAITS", typeof(double)); 

      dtTopAllTemp.Columns.Add("SAMPLE_TIME", typeof(DateTime)); 
      dtTopAllTemp.Columns.Add("INST_ID", typeof(int)); 
      dtTopAllTemp.Columns.Add("WAIT_CLASS", typeof(string)); 
      dtTopAllTemp.Columns.Add("EVENT", typeof(string)); 
      dtTopAllTemp.Columns.Add("WAITS", typeof(double)); 

      for (int i = 0; i < 10; i++) 
      { 
       dtTopAllTempOld.Rows.Add(DateTime.Now.AddDays(i), i, "Wait_Class " + i, "Event " + i, i*100); 
       dtTopAllTemp.Rows.Add(DateTime.Now.AddDays(i), i, "Wait_Class " + i, "Event " + i, i * 100); 
      } 
     } 


     //WAITS = Math.Round((dr2["WAITS"]==DBNULL.Value ? 0 : dr2.Field<double>("WAITS")) -(dr1["WAITS"]==DBNULL.Value ? 0 : dr1.Field<double>("WAITS")))/timeTopActivity) 

     private void button1_Click(object sender, EventArgs e) 
     { 
      var result = (from dr1 in dtTopAllTempOld.AsEnumerable() 
       from dr2 in dtTopAllTemp.AsEnumerable() 
       where dr1.Field<string>("EVENT") == dr2.Field<string>("EVENT") 
       select new 
       { 
        SAMPLE_TIME = dr1.Field<DateTime>("SAMPLE_TIME"), 
        INST_ID = dr1.Field<int>("INST_ID"), 
        WAIT_CLASS = dr1.Field<string>("WAIT_CLASS"), 
        EVENT = dr1.Field<string>("EVENT"), 
        WAITS = Math.Round((dr2.Field<double>("WAITS")) -(dr1.Field<double>("WAITS"))) 
       }).ToList(); 
     } 


    } 

我猜你是在减去双重价值得到这个例外，你需要减去，如果问题是与减法这可能会解决你的问题之前，检查空值，请检查该