我正在尝试将 MySqlDateTime 对象与另一个 MySqlDateTime 对象进行比较，每个对象都来自两个不同的表。我正在尝试在 LINQ 查询中执行所有这些操作，例如:

        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;

这给了我一个编译器错误:

运算符“==”不能应用于“MySql.Data.Types.MySqlDateTime”和“MySql.Data.Types.MySqlDateTime”类型的操作数

那么我试试这个:

        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;

现在可以编译了，但是我得到一个运行时错误:

指定的转换无效。

堆栈跟踪:

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]    

另一个我试过的例子:

            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;

仍然引发运行时错误:

指定的转换无效。

另一个例子:

            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;

同样的运行时错误:

指定的转换无效。

有人说“date”不是 MySqlDateTime 类型，为了好玩，这里是它的证明:

            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;

运行时异常:

无法将“MySql.Data.Types.MySqlDateTime”类型的对象转换为类型“System.String”。

我已经尝试了一些其他的东西，但对我来说没有任何效果。

如有任何帮助，我们将不胜感激

问候，

凯尔

最佳答案

最大的可能是DataRow的"date"字段不是MySqlDateTime类型，或者"device_id3" 字段不是 string 类型。

关于c# - LINQ 查询中的 MySqlDateTime，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/16654152/