错误：实体类型需要主键

我想扩展这个问题上提出的问题

将列表框绑定到observablecollection

通过赋予它持久化数据的能力。 除了我安装Entity Framework Core之外，结构大致相同，创建了一个DbContext类来保存记录。 我添加了一个按钮将数据集保存到SQL Server。 我没有遇到编译错误但是当我试图将数据保存在数据库中时，我得到了这个运行时exception：

Message =实体类型’Fruit’需要定义主键。

整个例外情况如下

System.InvalidOperationException未处理
的HResult = -2146233079
Message =实体类型’Fruit’需要定义主键。
来源= Microsoft.EntityFrameworkCore
堆栈跟踪：
在Microsoft.EntityFrameworkCore.Internal.ModelValidator.ShowError（String message）
在Microsoft.EntityFrameworkCore.Internal.ModelValidator.EnsureNonNullPrimaryKeys（IModel模型）
在Microsoft.EntityFrameworkCore.Internal.ModelValidator.Validate（IModel模型）
在Microsoft.EntityFrameworkCore.Internal.RelationalModelValidator.Validate（IModel模型）
在Microsoft.EntityFrameworkCore.Infrastructure.ModelSource.CreateModel（DbContext上下文，IConventionSetBuilder conventionSetBuilder，IModelValidatorvalidation器）
在Microsoft.EntityFrameworkCore.Infrastructure.ModelSource。 c__DisplayClass14_0.b__0（对象k）
在System.Collections.Concurrent.ConcurrentDictionary 2.GetOrAdd(TKey key, Func 2 valueFactory）
在Microsoft.EntityFrameworkCore.Infrastructure.ModelSource.GetModel（DbContext上下文，IConventionSetBuilder conventionSetBuilder，IModelValidatorvalidation器）
在Microsoft.EntityFrameworkCore.Internal.DbContextServices.CreateModel（）
在Microsoft.EntityFrameworkCore.Internal.LazyRef 1.get_Value()
at Microsoft.EntityFrameworkCore.Internal.DbContextServices.get_Model()
at Microsoft.EntityFrameworkCore.Infrastructure.EntityFrameworkServiceCollectionExtensions.c.b__0_6(IServiceProvider p)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactoryService(FactoryService factoryService, ServiceProvider provider)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor 1.get_Value()
at Microsoft.EntityFrameworkCore.Internal.DbContextServices.get_Model()
at Microsoft.EntityFrameworkCore.Infrastructure.EntityFrameworkServiceCollectionExtensions.c.b__0_6(IServiceProvider p)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactoryService(FactoryService factoryService, ServiceProvider provider)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor 1.get_Value()
at Microsoft.EntityFrameworkCore.Internal.DbContextServices.get_Model()
at Microsoft.EntityFrameworkCore.Infrastructure.EntityFrameworkServiceCollectionExtensions.c.b__0_6(IServiceProvider p)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactoryService(FactoryService factoryService, ServiceProvider provider)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor 2.VisitCallSite（IServiceCallSite callSite，TArgument参数）
在Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScoped（ScopedCallSite scopedCallSite，ServiceProvider provider）
在Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor 2.VisitCallSite(IServiceCallSite callSite, TArgument argument)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitConstructor(ConstructorCallSite constructorCallSite, ServiceProvider provider)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor 2.VisitCallSite(IServiceCallSite callSite, TArgument argument)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitConstructor(ConstructorCallSite constructorCallSite, ServiceProvider provider)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor 2.VisitCallSite(IServiceCallSite callSite, TArgument argument)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitConstructor(ConstructorCallSite constructorCallSite, ServiceProvider provider)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor 2.VisitCallSite（IServiceCallSite callSite，TArgument参数）
在Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScoped（ScopedCallSite scopedCallSite，ServiceProvider provider）
在Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor 2.VisitCallSite(IServiceCallSite callSite, TArgument argument)
at Microsoft.Extensions.DependencyInjection.ServiceProvider.c__DisplayClass16_0.b__0(ServiceProvider provider)
at Microsoft.Extensions.DependencyInjection.ServiceProvider.GetService(Type serviceType)
at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetService[T](IServiceProvider provider)
at Microsoft.EntityFrameworkCore.Infrastructure.AccessorExtensions.GetService[TService](IInfrastructure 2.VisitCallSite(IServiceCallSite callSite, TArgument argument)
at Microsoft.Extensions.DependencyInjection.ServiceProvider.c__DisplayClass16_0.b__0(ServiceProvider provider)
at Microsoft.Extensions.DependencyInjection.ServiceProvider.GetService(Type serviceType)
at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetService[T](IServiceProvider provider)
at Microsoft.EntityFrameworkCore.Infrastructure.AccessorExtensions.GetService[TService](IInfrastructure 2.VisitCallSite(IServiceCallSite callSite, TArgument argument)
at Microsoft.Extensions.DependencyInjection.ServiceProvider.c__DisplayClass16_0.b__0(ServiceProvider provider)
at Microsoft.Extensions.DependencyInjection.ServiceProvider.GetService(Type serviceType)
at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetService[T](IServiceProvider provider)
at Microsoft.EntityFrameworkCore.Infrastructure.AccessorExtensions.GetService[TService](IInfrastructure 1 accessor）
在Microsoft.EntityFrameworkCore.ChangeTracking.ChangeTracker.get_StateManager（）
在Microsoft.EntityFrameworkCore.ChangeTracking.ChangeTracker.DetectChanges（）
在Microsoft.EntityFrameworkCore.DbContext.TryDetectChanges（）
在Microsoft.EntityFrameworkCore.DbContext.SaveChanges（Boolean acceptAllChangesOnSuccess）
在Microsoft.EntityFrameworkCore.DbContext.SaveChanges（）
在Fruits：MainWindow.SaveFruitCommandBinding_Executed（Object sender，ExecutedRoutedEventArgs e）在D：\ Frank \ Test \ Fruits \ Fruits \ MainWindow.xaml.cs：第50行
在System.Windows.Input.CommandBinding.OnExecuted（Object sender，ExecutedRoutedEventArgs e）
在System.Windows.Input.CommandManager.ExecuteCommandBinding（Object sender，ExecutedRoutedEventArgs e，CommandBinding commandBinding）
在System.Windows.Input.CommandManager.FindCommandBinding（CommandBindingCollection commandBindings，Object sender，RoutedEventArgs e，ICommand command，Boolean execute）
在System.Windows.Input.CommandManager.FindCommandBinding（对象发送者，RoutedEventArgs e，ICommand命令，布尔执行）
at System.Windows.Input.CommandManager.OnExecuted（Object sender，ExecutedRoutedEventArgs e）at System.Windows.UIElement.OnExecutedThunk（Object sender，ExecutedRoutedEventArgs e）at System.Windows.Input.ExecutedRoutedEventArgs.InvokeEventHandler（Delegate genericHandler，Object target）at at系统中System.Windows.EventRoute.InvokeHandlersImpl（Object source，RoutedEventArgs args，Boolean reRaised）的System.Windows.RoutedEventHandlerInfo.InvokeHandler（Object target，RoutedEventArgs routedEventArgs）中的System.Windows.RoutedEventArgs.InvokeHandler（Delegate handler，Object target）。 System.Windows.UIElement.RaiseEvent（RoutedEventArgs args，布尔值受信任）的System.Windows.Input.RoutedCommand.ExecuteImpl（Object参数，IInputElement target，Boolean userInitiated）中的Windows.UIElement.RaiseEventImpl（DependencyObject sender，RoutedEventArgs args）。 MS.Internal.Commands.CommandHel中的Windows.Input.RoutedCommand.ExecuteCore（Object parameter，IInputElement target，Boolean userInitiated） System.Windows.Controls.Primitives.ButtonBase.OnMouseLeftButtonUp（MouseButtonEventArgs）中的System.Windows.Controls.Button.OnClick（）处的System.Windows.Controls.Primitives.ButtonBase.OnClick（）中的pers.CriticalExecuteCommandSource（ICommandSource commandSource，Boolean userInitiated） e）位于System.Windows.RindtedEventArgs.InvokeHandler（委托处理程序，对象目标）的System.Windows.Input.MouseButtonEventArgs.InvokeEventHandler（Delegate genericHandler，Object genericTarget）中的System.Windows.UIElement.OnMouseLeftButtonUpThunk（Object sender，MouseButtonEventArgs e）at at在System.Windows.UIElement.ReRaiseEventAs（DependencyObject sender，RoutedEventArgs args，RoutedEvent newEvent）的System.Windows.EventRoute.InvokeHandlersImpl（Object source，RoutedEventArgs args，Boolean reRaised）中的System.Windows.RoutedEventHandlerInfo.InvokeHandler（Object target，RoutedEventArgs routedEventArgs） System.Windows.Input.MouseButt上的System.Windows.UIElement.OnMouseUpThunk（Object sender，MouseButtonEventArgs e） System.Windows.EventRoute.InvokeHandlersImpl（Object）上的System.Windows.RoutedEventHandlerInfo.InvokeHandler（Object target，RoutedEventArgs routedEventArgs）上的System.Windows.RoutedEventArgs.InvokeHandler（Delegate handler，Object target）中的onEventArgs.InvokeEventHandler（Delegate genericHandler，Object genericTarget）在System.Windows.Uindlement.RaiseEvent（RoutedEventArgs args，布尔值受信任）的System.Windows.UIElement.RaiseTrustedEvent（RoutedEventArgs args）的System.Windows.UIElement.RaiseEventImpl（DependencyObject sender，RoutedEventArgs args）中的source，RoutedEventArgs args，Boolean reRaised）处于System.Windows.Inputop.HwndMouseInputProvider.ReportInput中System.Windows.Input.InputProviderSite.ReportInput（InputReport inputReport）的System.Windows.Input.InputManager.ProcessInput（InputEventArgs输入）中的System.Windows.Input.InputManager.ProcessStagingArea（） System.Windows.Interop.H上的（IntPtr hwnd，InputMode模式，Int32时间戳，RawMouseActions操作，Int32 x，Int32 y，Int32轮） 在MS.Win32的System.Windows.Interop.HwndSource.InputFilterMessage（IntPtr hwnd，Int32 msg，IntPtr wParam，IntPtr lParam，Boolean＆handling）中的wndMouseInputProvider.FilterMessage（IntPtr hwnd，WindowMessage msg，IntPtr wParam，IntPtr lParam，Boolean＆handling）。在System.Windows.Threading.ExceptionWrapper.InternalRealCall的MS.Win32.HwndSubclass.DispatcherCallbackOperation（Object o）中的HwndWrapper.WndProc（IntPtr hwnd，Int32 msg，IntPtr wParam，IntPtr lParam，Boolean＆handling）（委托回调，Object args，Int32 numArgs ）在System.Windows.Threading.Dispatcher.LegacyInvokeImpl的System.Windows.Threading.ExceptionWrapper.TryCatchWhen（Object source，Delegate callback，Object args，Int32 numArgs，Delegate catchHandler）中（DispatcherPriority优先级，TimeSpan超时，Delegate方法，Object args，位于System.Windows.Threading.Dispatch的MS.Win32.UnsafeNativeMethods.DispatchMessage（MSG＆msg）的MS.Win32.HwndSubclass.SubclassWndProc（IntPtr hwnd，Int32 msg，IntPtr wParam，IntPtr lParam）上的Int32 numArgs） System.Windows上的System.Windows.Application.RunInternal（窗口窗口）中的System.Windows.Application.RunDispatcher（Object ignore）处的System.Windows.Threading.Dispatcher.PushFrame（DispatcherFrame框架）中的er.PushFrameImpl（DispatcherFrame框架）。 System.AppDomain.ExecuteAssembly（String assemblyFile，证据assemblySecurity，String [] args）位于System.Threading.Thread上的Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly（）处于System.Threading.TereadStart_Context（Object状态），执行文件执行上下文（ExecutionContext executionContext，ContextCallback回调，对象状态， System.Threading.ExecutionContext.Run上的System.Threading.ExecutionContext.Run（ExecutionContext executionContext，ContextCallback回调，Object状态，Boolean preserveSyncCtx）中的Boolean preserveSyncCtx（ExecutionContext exec） System.Threading.ThreadHelper.ThreadStart（）中的utionContext，ContextCallback回调，对象状态InnerException：

这是更新的类Fruit：

 namespace Fruits.ViewModels { [Table("Fruits")] public class Fruit : ViewModelBase { #region Constractor public Fruit() { } public Fruit(string name, String clrString) { FruitName = name; // Parse colors like so: (Color)ColorConverter.ConvertFromString(clrString); FruitColor = clrString; _id = Guid.NewGuid(); } public Fruit(string name, Color clr) { FruitName = name; FruitColor = clr.ToString(); _id = Guid.NewGuid(); } #endregion #region Properties private Guid _id; [Key] public Guid ID { get { return _id; } } #region FruitName private string _fruitname; public string FruitName { get { return _fruitname; } set { if (_fruitname != value) { _fruitname = value; OnPropertyChanged("FruitName"); } } } #endregion #region FruitColor private String _fruitcolor; public String FruitColor { get { return _fruitcolor; } set { if (_fruitcolor != value) { _fruitcolor = value; OnPropertyChanged("FruitColor"); } } } #endregion #region Selected Property private bool _isSelected = true; // NOTE: I renamed this property public bool IsSelected { get { return _isSelected; } set { if (_isSelected != value) { _isSelected = value; OnPropertyChanged("IsSelected"); } } } #endregion #endregion } } 

更新的MainWindows xaml（添加保存按钮）

            Selected Fruit Only   New Name:    New Color: <!---->           

和我在mainwindows后面的代码（添加处理程序）

 using Fruits.ViewModels; using System; using System.Windows; using System.Windows.Input; namespace Fruits { /// 
 /// Interaction logic for MainWindow.xaml /// 
 public partial class MainWindow : Window { public MainWindow() { InitializeComponent(); DataContext = new MainViewModel(); ViewModel.AddNewFruit("Jackfruit", "Yellow"); ViewModel.AddNewFruit("Watermelon", "ForestGreen"); ViewModel.AddNewFruit("Apple", "Red"); ViewModel.AddNewFruit("Banana", "Yellow"); ViewModel.AddNewFruit("Orange", "DeepSkyBlue"); //ViewModel.Fruits[0].IsSelected = false; //ViewModel.Fruits[1].IsSelected = false; ViewModel.FruitsView.Refresh(); } public MainViewModel ViewModel { get { return DataContext as MainViewModel; } } private void AddFruitCommandBinding_Executed(object sender, ExecutedRoutedEventArgs e) { ViewModel.AddNewFruit(); } private void AddFruitCommandBinding_CanExecute(object sender, CanExecuteRoutedEventArgs e) { e.CanExecute = ViewModel != null && !String.IsNullOrWhiteSpace(ViewModel.NewFruitName) && !String.IsNullOrWhiteSpace(ViewModel.NewFruitColor) ; } private void SaveFruitCommandBinding_Executed(object sender, ExecutedRoutedEventArgs e) { using (var db=new FruitDbContext()) { db.SaveChanges(); } } private void SaveFruitCommandBinding_CanExecute(object sender, CanExecuteRoutedEventArgs e) { e.CanExecute = true; } } } 

我新添加的dbContext：

 namespace Fruits.ViewModels { public class FruitDbContext:DbContext { public DbSet Fruits { get; set; } protected override void OnConfiguring(DbContextOptionsBuilder optionBuilder) { optionBuilder.UseSqlServer(@"Server = xxx; Database=Test; Integrated Security = True"); } } } 

其他类保持不变，但无论如何我列出了它们：

ViewModelBase

  namespace Fruits.ViewModels { public class ViewModelBase : INotifyPropertyChanged { public event PropertyChangedEventHandler PropertyChanged; public void OnPropertyChanged(string name) { if (PropertyChanged != null) { PropertyChanged(this, new PropertyChangedEventArgs(name)); } } } } ViewModel using System; using System.Collections.ObjectModel; using System.ComponentModel; using System.Windows.Data; using System.Windows.Media; namespace Fruits.ViewModels { #region MainViewModel Class public class MainViewModel : ViewModelBase { public MainViewModel() { Fruits = new ObservableCollection(); } public ICollectionView FruitsView { get; private set; } #region ShowSelectedFruitOnly Property private bool _showSelectedFruitOnly = true; public bool ShowSelectedFruitOnly { get { return _showSelectedFruitOnly; } set { if (value != _showSelectedFruitOnly) { _showSelectedFruitOnly = value; FruitsView.Refresh(); OnPropertyChanged("ShowSelectedFruitOnly"); } } } #endregion ShowSelectedFruitOnly Property #region Add Methods public void AddNewFruit() { Fruits.Add(new Fruit(NewFruitName, NewFruitColor)); NewFruitName = ""; NewFruitColor = ""; } public void AddNewFruit(string name, string color) { Fruits.Add(new Fruit(name, color)); } public void AddNewFruit(string name, Color color) { Fruits.Add(new Fruit(name, color)); } #endregion Add Methods #region NewFruitName Property private String _newFruitName = default(String); public String NewFruitName { get { return _newFruitName; } set { if (value != _newFruitName) { _newFruitName = value; OnPropertyChanged("NewFruitName"); } } } #endregion NewFruitName Property #region NewFruitColor Property private String _newFruitColor = default(String); public String NewFruitColor { get { return _newFruitColor; } set { if (value != _newFruitColor) { _newFruitColor = value; OnPropertyChanged("NewFruitColor"); } } } #endregion NewFruitColor Property #region Fruits Property private static ObservableCollection _fruits; public ObservableCollection Fruits { get { return _fruits; } private set { if (value != _fruits) { _fruits = value; FruitsView = CollectionViewSource.GetDefaultView(Fruits); FruitsView.Filter = FruitFilterPredicate; FruitsView.Refresh(); OnPropertyChanged("Fruits"); } } } protected bool FruitFilterPredicate(Object o) { if (ShowSelectedFruitOnly) { return (o as Fruit).IsSelected; } return true; } #endregion Fruits Property } #endregion MainViewModel Class } 

App.xaml中

我项目的结构

我在SQL Server中的表：

 CREATE TABLE [dbo].[Fruits] ( [ID] [uniqueidentifier] NOT NULL, [FruitName] [nvarchar](50) NULL, [FruitColor] [nvarchar](50) NULL, [IsSelected] [nvarchar](1) NULL, CONSTRAINT [PK_Fruit] PRIMARY KEY CLUSTERED ([ID] ASC) WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] ) ON [PRIMARY] 

请告知为什么消息说它确实存在时没有主键

Answer 1

此exception消息并不意味着它需要在数据库中定义主键，这意味着它需要在您的类中定义主键。

虽然你试图这样做：

 private Guid _id; [Key] public Guid ID { get { return _id; } } 

这没有任何效果，因为entity framework忽略只读属性。 它必须：当它从数据库中检索Fruits记录时，它构造一个Fruit对象，然后为每个映射的属性调用属性setter。 这对于只读属性永远不会起作用。

您需要Entity Framework才能设置ID的值。 这意味着该物业需要一个二传手。

Answer 2

我带着类似的错误来到这里：

System.InvalidOperationException：’实体类型’MyType’需要定义主键。

在读完hvd的回答之后，意识到我只是忘了让我的关键财产“公开”。 这个..

 namespace MyApp.Models.Schedule { public class MyType { [Key] int Id { get; set; } // ... 

应该是这个..

 namespace MyApp.Models.Schedule { public class MyType { [Key] public int Id { get; set; } // must be public! // ...