5

I am trying to do a comparison of a MySqlDateTime object to another MySqlDateTime object, each from two different tables. I am trying to do all of this inside a LINQ query, ex:

        var prodRowFindQuery =
            from x in production.AsEnumerable()
            where x.Field<MySqlDateTime>("date") == row.Field<MySqlDateTime>("date") &&
                  x.Field<String>("device_id3") == row.Field<String>("device_id3")
            select x;

This gives me a compiler error:

Operator '==' cannot be applied to operands of type 'MySql.Data.Types.MySqlDateTime' and 'MySql.Data.Types.MySqlDateTime'

So then I try this:

        var prodRowFindQuery =
            from x in production.AsEnumerable()
            where x.Field<MySqlDateTime>("date").ToString() == row.Field<MySqlDateTime>("date").ToString() &&
                  x.Field<String>("device_id3") == row.Field<String>("device_id3")
            select x;

Now it compiles, but I get a run-time error:

Specified cast is not valid.

Stack Trace: 

IthacaDbTransferUtil.exe!IthacaDbTransferUtil.DataTableComparer.CompareTables.AnonymousMethod__0(System.Data.DataRow x = {System.Data.DataRow}) Line 34 C#  
System.Core.dll!System.Linq.Enumerable.WhereEnumerableIterator<System.Data.DataRow>.MoveNext() + 0x9c bytes   
IthacaDbTransferUtil.exe!IthacaDbTransferUtil.DataTableComparer.CompareTables(System.Data.DataTable aggregate = {System.Data.DataTable}, System.Data.DataTable production = {System.Data.DataTable}) Line 39 + 0x8b bytes   C#  
IthacaDbTransferUtil.exe!IthacaDbTransferUtil.DbTransferWindowViewModel.CopyTestReliability() Line 177 + 0x94 bytes C#  
IthacaDbTransferUtil.exe!IthacaDbTransferUtil.DelegateCommand.Execute() Line 78 + 0x1f bytes    C#  
IthacaDbTransferUtil.exe!IthacaDbTransferUtil.DelegateCommand.System.Windows.Input.ICommand.Execute(object parameter = null) Line 158 + 0xa bytes   C#  
PresentationFramework.dll!System.Windows.Controls.Button.OnClick() + 0xaf bytes   
PresentationFramework.dll!System.Windows.Controls.Primitives.ButtonBase.OnMouseLeftButtonUp(System.Windows.Input.MouseButtonEventArgs e) + 0x117 bytes    
PresentationCore.dll!System.Windows.RoutedEventArgs.InvokeHandler(System.Delegate handler, object target) + 0x56 bytes    
PresentationCore.dll!System.Windows.EventRoute.InvokeHandlersImpl(object source, System.Windows.RoutedEventArgs args, bool reRaised) + 0x270 bytes    
PresentationCore.dll!System.Windows.UIElement.ReRaiseEventAs(System.Windows.DependencyObject sender = {System.Windows.Controls.Button}, System.Windows.RoutedEventArgs args = {System.Windows.Input.MouseButtonEventArgs}, System.Windows.RoutedEvent newEvent) + 0x183 bytes     
PresentationCore.dll!System.Windows.RoutedEventArgs.InvokeHandler(System.Delegate handler, object target) + 0x56 bytes    
PresentationCore.dll!System.Windows.EventRoute.InvokeHandlersImpl(object source, System.Windows.RoutedEventArgs args, bool reRaised) + 0x270 bytes    
PresentationCore.dll!System.Windows.UIElement.RaiseEventImpl(System.Windows.DependencyObject sender = {System.Windows.Controls.Button}, System.Windows.RoutedEventArgs args = {System.Windows.Input.MouseButtonEventArgs}) + 0x14e bytes  
PresentationCore.dll!System.Windows.UIElement.RaiseTrustedEvent(System.Windows.RoutedEventArgs args = {System.Windows.Input.MouseButtonEventArgs}) + 0x64 bytes   
PresentationCore.dll!System.Windows.Input.InputManager.ProcessStagingArea() + 0x431 bytes     
PresentationCore.dll!System.Windows.Input.InputProviderSite.ReportInput(System.Windows.Input.InputReport inputReport) + 0xfd bytes    
PresentationCore.dll!System.Windows.Interop.HwndMouseInputProvider.ReportInput(System.IntPtr hwnd, System.Windows.Input.InputMode mode, int timestamp, System.Windows.Input.RawMouseActions actions, int x, int y, int wheel) + 0x410 bytes   
PresentationCore.dll!System.Windows.Interop.HwndMouseInputProvider.FilterMessage(System.IntPtr hwnd = 396436, MS.Internal.Interop.WindowMessage msg = WM_LBUTTONUP, System.IntPtr wParam = 0, System.IntPtr lParam = 34472260, ref bool handled = false) + 0x388 bytes    
PresentationCore.dll!System.Windows.Interop.HwndSource.InputFilterMessage(System.IntPtr hwnd, int msg, System.IntPtr wParam, System.IntPtr lParam, ref bool handled) + 0x7c bytes  
WindowsBase.dll!MS.Win32.HwndWrapper.WndProc(System.IntPtr hwnd, int msg, System.IntPtr wParam, System.IntPtr lParam, ref bool handled) + 0x14a bytes     
WindowsBase.dll!MS.Win32.HwndSubclass.DispatcherCallbackOperation(object o) + 0x80 bytes      
WindowsBase.dll!System.Windows.Threading.ExceptionWrapper.InternalRealCall(System.Delegate callback, object args, int numArgs) + 0x5e bytes  
WindowsBase.dll!MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(object source = {System.Windows.Threading.Dispatcher}, System.Delegate method, object args, int numArgs, System.Delegate catchHandler = null) + 0x47 bytes  
WindowsBase.dll!System.Windows.Threading.Dispatcher.LegacyInvokeImpl(System.Windows.Threading.DispatcherPriority priority, System.TimeSpan timeout, System.Delegate method, object args, int numArgs) + 0x2bc bytes  
WindowsBase.dll!MS.Win32.HwndSubclass.SubclassWndProc(System.IntPtr hwnd, int msg, System.IntPtr wParam, System.IntPtr lParam) + 0x140 bytes      
[Native to Managed Transition]    
[Managed to Native Transition]    
WindowsBase.dll!System.Windows.Threading.Dispatcher.PushFrameImpl(System.Windows.Threading.DispatcherFrame frame) + 0x112 bytes   
PresentationFramework.dll!System.Windows.Application.RunInternal(System.Windows.Window window) + 0x17a bytes      
PresentationFramework.dll!System.Windows.Application.Run() + 0x67 bytes   
IthacaDbTransferUtil.exe!IthacaDbTransferUtil.App.Main() + 0x77 bytes   C#  
[Native to Managed Transition]    
[Managed to Native Transition]    
Microsoft.VisualStudio.HostingProcess.Utilities.dll!Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly() + 0x5a bytes    
mscorlib.dll!System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state, bool preserveSyncCtx) + 0x285 bytes   
mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state, bool preserveSyncCtx) + 0x9 bytes     
mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state) + 0x57 bytes      
mscorlib.dll!System.Threading.ThreadHelper.ThreadStart() + 0x51 bytes     
[Native to Managed Transition]

Another example I have tried:

            var prodRowFindQuery =
                from x in production.AsEnumerable()
                where Convert.ToDateTime(x.Field<MySqlDateTime>("date")) == Convert.ToDateTime(row.Field<MySqlDateTime>("date")) &&
                      x.Field<String>("device_id3") == row.Field<String>("device_id3")
                select x;

Still raises a run-time error:

Specified cast is not valid.

Another example:

            var prodRowFindQuery =
                from x in production.AsEnumerable()
                where x.Field<DateTime>("date") == row.Field<DateTime>("date") &&
                      x.Field<String>("device_id3") == row.Field<String>("device_id3")
                select x;

Same run-time error:

Specified cast is not valid.

Somebody said something about "date" not being a MySqlDateTime type, for fun, here's the proof that it is:

            var prodRowFindQuery =
                from x in production.AsEnumerable()
                where x.Field<String>("date") == row.Field<String>("date") &&
                      x.Field<String>("device_id3") == row.Field<String>("device_id3")
                select x;

Run-time exception:

Unable to cast object of type 'MySql.Data.Types.MySqlDateTime' to type 'System.String'.

I have tried a few other things and nothing works for me.

Any help would be greatly appreciated,

Regards,

Kyle

4

3 回答 3

0

我终于解决了这个问题。

在伪代码中，我是这样做的：

  1. 创建两个新的数据表
  2. 对一个 DataTable 进行选择，提取该表所需的所有数据

  3. 通过执行以下操作克隆表：

        officialTable = temporaryTable.Clone();

  4. 通过执行以下操作强制转换列：

        officialTable.Columns["date"].DataType = typeof(String);

  5. 要么遍历表行，将一行复制到另一行；或者执行另一个 select 语句以再次获取所有数据，但这一次，“数据”列将自动转换为 a 而不是 .

  6. 处理旧的 DataTable

我希望这可以帮助其他人。

于 2013-06-10T20:41:33.667 回答
0

最高概率是"date"字段 of DataRowis not of type MySqlDateTime，或者"device_id3"field is not of type string。

于 2013-05-20T18:16:23.047 回答
0

如果没有为 MySQLDateTime 定义相等运算符，您可以自己定义一个，或者在进行比较之前将其转换为标准的 .NET datetime 对象。

于 2013-05-20T18:53:07.963 回答