Error: the entity type requires a primary key

I would like to expand the question asked on this thread

Binding listbox to observablecollection

by giving it an ability to persistent the data. The structure is mostly the same except I installed Entity Framework Core, created a DbContext class to hold the records. I added a button to save the dataset to SQL Server. I did not encounter the compiling error but when I attempted to save the data in the database I got this run time exception:

> Message=The entity type 'Fruit' requires a primary key to be defined.

The whole exception in its entirety is listed below

> System.InvalidOperationException was unhandled
> HResult=-2146233079
> Message=The entity type 'Fruit' requires a primary key to be defined.
> Source=Microsoft.EntityFrameworkCore
> StackTrace:
> at Microsoft.EntityFrameworkCore.Internal.ModelValidator.ShowError(String message)
> at Microsoft.EntityFrameworkCore.Internal.ModelValidator.EnsureNonNullPrimaryKeys(IModel model)
> at Microsoft.EntityFrameworkCore.Internal.ModelValidator.Validate(IModel model)
> at Microsoft.EntityFrameworkCore.Internal.RelationalModelValidator.Validate(IModel model)
> at Microsoft.EntityFrameworkCore.Infrastructure.ModelSource.CreateModel(DbContext context, IConventionSetBuilder conventionSetBuilder, IModelValidator validator)
> at Microsoft.EntityFrameworkCore.Infrastructure.ModelSource.<>c__DisplayClass14_0.b__0(Object k)
> at System.Collections.Concurrent.ConcurrentDictionary2.GetOrAdd(TKey key, Func2 valueFactory)
> at Microsoft.EntityFrameworkCore.Infrastructure.ModelSource.GetModel(DbContext context, IConventionSetBuilder conventionSetBuilder, IModelValidator validator)
> at Microsoft.EntityFrameworkCore.Internal.DbContextServices.CreateModel()
> at Microsoft.EntityFrameworkCore.Internal.LazyRef1.get_Value() > at Microsoft.EntityFrameworkCore.Internal.DbContextServices.get_Model() > at Microsoft.EntityFrameworkCore.Infrastructure.EntityFrameworkServiceCollectionExtensions.<>c.<AddEntityFramework>b__0_6(IServiceProvider p) > at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactoryService(FactoryService factoryService, ServiceProvider provider) > at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor2.VisitCallSite(IServiceCallSite callSite, TArgument argument)
> at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScoped(ScopedCallSite scopedCallSite, ServiceProvider provider)
> at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor2.VisitCallSite(IServiceCallSite callSite, TArgument argument) > at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitConstructor(ConstructorCallSite constructorCallSite, ServiceProvider provider) > at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor2.VisitCallSite(IServiceCallSite callSite, TArgument argument)
> at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScoped(ScopedCallSite scopedCallSite, ServiceProvider provider)
> at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor2.VisitCallSite(IServiceCallSite callSite, TArgument argument) > at Microsoft.Extensions.DependencyInjection.ServiceProvider.<>c__DisplayClass16_0.<RealizeService>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](IInfrastructure1 accessor)
> at Microsoft.EntityFrameworkCore.ChangeTracking.ChangeTracker.get_StateManager()
> at Microsoft.EntityFrameworkCore.ChangeTracking.ChangeTracker.DetectChanges()
> at Microsoft.EntityFrameworkCore.DbContext.TryDetectChanges()
> at Microsoft.EntityFrameworkCore.DbContext.SaveChanges(Boolean acceptAllChangesOnSuccess)
> at Microsoft.EntityFrameworkCore.DbContext.SaveChanges()
> at Fruits.MainWindow.SaveFruitCommandBinding_Executed(Object sender, ExecutedRoutedEventArgs e) in D:\Frank\Test\Fruits\Fruits\MainWindow.xaml.cs:line 50
> at System.Windows.Input.CommandBinding.OnExecuted(Object sender, ExecutedRoutedEventArgs e)
> at System.Windows.Input.CommandManager.ExecuteCommandBinding(Object sender, ExecutedRoutedEventArgs e, CommandBinding commandBinding)
> at System.Windows.Input.CommandManager.FindCommandBinding(CommandBindingCollection commandBindings, Object sender, RoutedEventArgs e, ICommand command, Boolean execute)
> at System.Windows.Input.CommandManager.FindCommandBinding(Object sender, RoutedEventArgs e, ICommand command, Boolean execute)
> 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 System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target) at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs) at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised) at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args) at System.Windows.UIElement.RaiseEvent(RoutedEventArgs args, Boolean trusted) at System.Windows.Input.RoutedCommand.ExecuteImpl(Object parameter, IInputElement target, Boolean userInitiated) at System.Windows.Input.RoutedCommand.ExecuteCore(Object parameter, IInputElement target, Boolean userInitiated) at MS.Internal.Commands.CommandHelpers.CriticalExecuteCommandSource(ICommandSource commandSource, Boolean userInitiated) at System.Windows.Controls.Primitives.ButtonBase.OnClick() at System.Windows.Controls.Button.OnClick() at System.Windows.Controls.Primitives.ButtonBase.OnMouseLeftButtonUp(MouseButtonEventArgs e) at System.Windows.UIElement.OnMouseLeftButtonUpThunk(Object sender, MouseButtonEventArgs e) at System.Windows.Input.MouseButtonEventArgs.InvokeEventHandler(Delegate genericHandler, Object genericTarget) at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target) at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs) at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised) at System.Windows.UIElement.ReRaiseEventAs(DependencyObject sender, RoutedEventArgs args, RoutedEvent newEvent) at System.Windows.UIElement.OnMouseUpThunk(Object sender, MouseButtonEventArgs e) at System.Windows.Input.MouseButtonEventArgs.InvokeEventHandler(Delegate genericHandler, Object genericTarget) at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target) at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs) at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised) at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args) at System.Windows.UIElement.RaiseTrustedEvent(RoutedEventArgs args) at System.Windows.UIElement.RaiseEvent(RoutedEventArgs args, Boolean trusted) at System.Windows.Input.InputManager.ProcessStagingArea() at System.Windows.Input.InputManager.ProcessInput(InputEventArgs input) at System.Windows.Input.InputProviderSite.ReportInput(InputReport inputReport) at System.Windows.Interop.HwndMouseInputProvider.ReportInput(IntPtr hwnd, InputMode mode, Int32 timestamp, RawMouseActions actions, Int32 x, Int32 y, Int32 wheel) at System.Windows.Interop.HwndMouseInputProvider.FilterMessage(IntPtr hwnd, WindowMessage msg, IntPtr wParam, IntPtr lParam, Boolean& handled) at System.Windows.Interop.HwndSource.InputFilterMessage(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled) at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled) at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o) at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs) at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler) at System.Windows.Threading.Dispatcher.LegacyInvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs) at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam) at MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg) at System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame) at System.Windows.Threading.Dispatcher.PushFrame(DispatcherFrame frame) at System.Windows.Application.RunDispatcher(Object ignore) at System.Windows.Application.RunInternal(Window window) at System.Windows.Application.Run(Window window) at System.Windows.Application.Run() at Fruits.App.Main() at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args) at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args) at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly() at System.Threading.ThreadHelper.ThreadStart_Context(Object state) at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ThreadHelper.ThreadStart() InnerException:

This is the updated class 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
	}
}

The updated MainWindows xaml (to add a save button)

<Window x:Class="Fruits.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:Fruits"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
	<Window.Resources>
		<RoutedCommand x:Key="AddFruit" />
		<RoutedCommand x:Key='SaveFruit' />
	</Window.Resources>
	<Window.CommandBindings>
		<CommandBinding Command='{StaticResource AddFruit}'
										Executed='AddFruitCommandBinding_Executed'
										CanExecute='AddFruitCommandBinding_CanExecute' />
		<CommandBinding Command='{StaticResource SaveFruit}'
										Executed='SaveFruitCommandBinding_Executed'
										CanExecute='SaveFruitCommandBinding_CanExecute' />
	</Window.CommandBindings>
	<Grid>
		<StackPanel Orientation='Vertical'
								Margin='10'>
			<CheckBox IsChecked="{Binding ShowSelectedFruitOnly}">Selected Fruit Only</CheckBox>
			<ListBox x:Name='MyList'
							 ItemsSource="{Binding FruitsView}"
							 ItemTemplate='{StaticResource FruitTemp}' />
			<StackPanel Orientation="Horizontal"
									Margin="0,10,0,0">
				<Label Width="100">New Name:</Label>
				<TextBox Width="200"
								 Text="{Binding NewFruitName, Mode=TwoWay }" 
								 />
			</StackPanel>
			<StackPanel Orientation="Horizontal"
									Margin="0,10,0,0">
				<Label Width="100">New Color:</Label>
				<!--<TextBox Width="200"
								 Text="{Binding NewFruitColor, UpdateSourceTrigger=PropertyChanged}" />-->
				<TextBox Width="200"
								 Text="{Binding NewFruitColor, Mode=TwoWay }" />

				<ContentControl Style="{StaticResource ColorSwatch}"
												Margin="2"
												VerticalAlignment="Center"
												Content="{Binding NewFruitColor}" />
			</StackPanel>
			<StackPanel Orientation='Horizontal'>
			<Button x:Name='AddFruit'
							Height='auto'
							Width='auto'
							Content='Add New Fruit 2'
							Margin='0,10,0,0'
							Command='{StaticResource AddFruit}' />
				<Button x:Name='SaveFruit'
								Height='auto'
								Width='auto'
								Content='Save Fruit'
								Margin='100,10,0,0'
								Command='{StaticResource SaveFruit}' />
			</StackPanel>
		</StackPanel>
	</Grid>
</Window>

and my code behind the mainwindows (added handler)

using Fruits.ViewModels;
using System;
using System.Windows;
using System.Windows.Input;

namespace Fruits
{
	/// <summary>
	/// Interaction logic for MainWindow.xaml
	/// </summary>
	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;
		}
	}
}

My newly added dbContext:

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

Other classes remain unchanged, but I listed them anyway:

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<Fruit>();

		}
		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<Fruit> _fruits;
		public ObservableCollection<Fruit> 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

<Application x:Class="Fruits.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:local="clr-namespace:Fruits"
             StartupUri="MainWindow.xaml">
    <Application.Resources>
		<Style x:Key="ColorSwatch"
					 TargetType="ContentControl">
			<Setter Property="Width"
							Value="24" />
			<Setter Property="Height"
							Value="24" />
			<Setter Property="IsTabStop"
							Value="false" />
			<Setter Property="ContentTemplate">
				<Setter.Value>
					<DataTemplate>
						<Rectangle HorizontalAlignment="Stretch"
											 VerticalAlignment="Stretch"
											 Stroke="Gray"
											 StrokeThickness="1">
							<Rectangle.Fill>
								<SolidColorBrush Color="{Binding}" />
							</Rectangle.Fill>
						</Rectangle>
					</DataTemplate>
				</Setter.Value>
			</Setter>
		</Style>

		<DataTemplate x:Key='FruitTemp'>
			<StackPanel Orientation='Horizontal'
									Margin='5'>
				<TextBlock x:Name='tbName'
									 Text='{Binding FruitName}'
									 Margin='10,0,0,0'
									 Width='100' />
				<TextBlock x:Name='tbColor'
									 Text='{Binding FruitColor}'
									 Margin='10,0,0,0'
									 Width='100' />
				<ContentControl Width="16"
												Height="16"
												Style="{StaticResource ColorSwatch}"
												Content="{Binding FruitColor}" />
				<!-- The problem here was you were trying to bind Checked, an event, 
                instead if IsChecked, a bool? property. 
                -->
				<CheckBox x:Name='cbSelected'
									Content='Selected'
									Margin='10,0,0,0'
									IsChecked='{Binding IsSelected}' />
			</StackPanel>
		</DataTemplate>
	</Application.Resources>
</Application>

The structure of my project

My table in SQL Server:

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]

Please advise why the message said there was no primary key while it does exist

This exception message doesn't mean it requires a primary key to be defined in your database, it means it requires a primary key to be defined in your class.

Although you've attempted to do so:

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

This has no effect, as Entity Framework ignores read-only properties. It has to: when it retrieves a Fruits record from the database, it constructs a Fruit object, and then calls the property setters for each mapped property. That's never going to work for read-only properties.

You need Entity Framework to be able to set the value of ID. This means the property needs to have a setter.

I came here with similar error:

> System.InvalidOperationException: 'The entity type 'MyType' requires a primary key to be defined.'

After reading answer by hvd, realized I had simply forgotten to make my key property 'public'. This..

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

        // ...

Should be this..

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

        // ...

I found a bit different cause of the error. It seems like SQLite wants to use correct primary key class property name. So...

Wrong PK name

public class Client
{
  public int SomeFieldName { get; set; }  // It is the ID
  ...
}

Correct PK name

public class Client
{
  public int Id { get; set; }  // It is the ID
  ...
}

public class Client
{
  public int ClientId { get; set; }  // It is the ID
  ...
}

It still posible to use wrong PK name but we have to use [Key] attribute like

public class Client
{
   [Key]
   public int SomeFieldName { get; set; }  // It is the ID
   ...
}

This worked for me:

using System.ComponentModel.DataAnnotations;

[Key]
public int ID { get; set; }

Make sure you have the following condition:

1. Use [key] if your primary key name is not Id or ID.
2. Use the public keyword.
3. Primary key should have getter and setter.

Example:

public class MyEntity {
   [key]
   public Guid Id {get; set;}
}

If you get the error:

> The entity type 'DeviceFlowCodes' requires a primary key to be > defined. If you intended to use a keyless entity type, call 'HasNoKey' > in 'OnModelCreating'. For more information on keyless entity types, > see https://go.microsoft.com/fwlink/?linkid=2141943.

You are probably using a solution with Individual User Accounts and have used protected override void OnModelCreating(ModelBuilder modelBuilder) in ApplicationDbContext.

The error comes from ApiAuthorizationDbContext that has a public DbSet<DeviceFlowCodes> DeviceFlowCodes { get; set; }.

Solve the error by calling base.OnModelCreating(modelBuilder); in protected override void OnModelCreating.

Source:

https://github.com/IdentityServer/IdentityServer4/issues/3169

Your Id property needs to have a setter. However the setter can be private. The [Key] attribute is not necessary if the property is named "Id" as it will find it through the naming convention where it looks for a key with the name "Id".

public Guid Id { get; }              // Will not work
public Guid Id { get; set; }         // Will work
public Guid Id { get; private set; } // Will also work

When I used the Scaffold-DbContext command, it didn't include the "[key]" annotation in the model files or the "entity.HasKey(..)" entry in the "modelBuilder.Entity" blocks. My solution was to add a line like this in every "modelBuilder.Entity" block in the *Context.cs file:

entity.HasKey(X => x.Id);

I'm not saying this is better, or even the right way. I'm just saying that it worked for me.

Yet another reason may be that your entity class has several properties named somhow /.*id/i - so ending with ID case insensitive AND elementary type AND there is no [Key] attribute.

EF will namely try to figure out the PK by itself by looking for elementary typed properties ending in ID.

See my case:

public class MyTest, IMustHaveTenant
{
  public long Id { get; set; }
  public int TenantId { get; set; }
  [MaxLength(32)]
  public virtual string Signum{ get; set; }
  public virtual string ID { get; set; }
  public virtual string ID_Other { get; set; }
}

don't ask - lecacy code. The Id was even inherited, so I could not use [Key] (just simplifying the code here)

But here EF is totally confused.

What helped was using modelbuilder this in DBContext class.

            modelBuilder.Entity<MyTest>(f =>
            {
                f.HasKey(e => e.Id);
                f.HasIndex(e => new { e.TenantId });
                f.HasIndex(e => new { e.TenantId, e.ID_Other });
            });

the index on PK is implicit.

I happened to have tried everything:

• made sure the property has a setter
• tried using the [Key] annotation
• used a property named "Id" with and without the [Key] annotation.

None of these worked, for a simple reason: my database was unavailable.

Fixing the connection to the database solved the "requires a primary key" issue.

(Weird that it's this error that shows even in that case.)

> The entity type 'DisplayFormatAttribute' requires a primary key to be > defined.

In my case I figured out the problem was that I used properties like this:

public string LastName { get; set; }  //OK
public string Address { get; set; }   //OK 
public string State { get; set; }     //OK
public int? Zip { get; set; }         //OK
public EmailAddressAttribute Email { get; set; } // NOT OK
public PhoneAttribute PhoneNumber { get; set; }  // NOT OK

Not sure if there is a better way to solve it but I changed the Email and PhoneNumber attribute to a string. Problem solved.

None of the answers worked until I removed the HasNoKey() method from the entity. Dont forget to remove this from your data context or the [Key] attribute will not fix anything.

Removed and added back in the table using Scaffold-DbContext and the error went away

In the DBContext I had this <List> code causing the error:

    public DbSet<List<<Item>> Items { get; set; } = null!;

You can get around it by making another class, I made a class ListItem that has a List<Item> in it and then declare both:

    public DbSet<Item> Items { get; set; } = null!;


    public DbSet<ListItem> ListItems { get; set; } = null!;

If you're using FluentApi make sure you're applying your configuration class like this:

internal class MyModelConfiguration : IEntityTypeConfiguration<MyModel>
    {
        public void Configure(EntityTypeBuilder<MyModel> builder)
        {
            builder.ToView("MyView", "dbo");
            ...
    
protected void OnModelCreating(ModelBuilder modelBuilder)
        {           
            modelBuilder.ApplyConfiguration(new MyConfiguration());
            ...