如何在 Entity Framework Core 中使用抽象 class？

Question

Starting out with EF Core, I'm trying to use an abstract class. I understand that I can't instantiate an abstract class and have a part of code missing but cannot find how to solve it.

The code is as follows:

using System;
using Microsoft.EntityFrameworkCore;
using System.ComponentModel.DataAnnotations;
using Microsoft.Extensions.Logging;

namespace ProjectTest1 
{
    public abstract class User 
    {
        [Key]
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string Password { get; set; }
        public string Email { get; set; }
        public bool IsAdmin { get; set; }
    }

    public class Student : User 
    {
        public string Number { get; set; }
    }

    public class Teacher : User 
    {
        public int Salary { get; set; }
    }

    public class Model : DbContext 
    {
        public static readonly ILoggerFactory _loggerFactory = LoggerFactory.Create(builder => {
            builder.AddConsole();
        });

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder) {
            base.OnConfiguring(optionsBuilder);
            optionsBuilder.UseSqlServer(@"Server=(localdb)\mssqllocaldb;Database=project")
                .EnableSensitiveDataLogging()
                .UseLoggerFactory(_loggerFactory);
        }

        public DbSet<User> Users { get; set; }
    }

    class Program 
    {
        static void Main(string[] args) 
        {
            using var model = new Model();
            model.Database.EnsureCreated();

            model.Users.RemoveRange(model.Users);
            model.SaveChanges();

            var guillaume = new Student() 
            {
                FirstName = "guillaume", 
                LastName = "b", 
                Password = "azerty",
                Email = "guillaume@gmail.com", 
                IsAdmin = true,
                Number = "150200"
            };

            var donald = new Teacher() 
            {
                FirstName = "donald", 
                LastName = "c", 
                Password = "azerty",
                Email = "donald@gmail.com", 
                IsAdmin = false, 
                Salary = 35000
            };

            model.Users.AddRange(new User[] { guillaume, donald });
            model.SaveChanges();
        }
    }
}

The execution of the code produce error:

System.InvalidOperationException
HResult=0x80131509

Message=The corresponding CLR type for entity type 'User' cannot be instantiated, and there is no derived entity type in the model that corresponds to a concrete CLR type.

Source=Microsoft.EntityFrameworkCore

StackTrace:

at Microsoft.EntityFrameworkCore.Infrastructure.ModelValidator.ValidateClrInheritance(IModel model, IEntityType entityType, HashSet 1 validEntityTypes) at Microsoft.EntityFrameworkCore.Infrastructure.ModelValidator.ValidateClrInheritance(IModel model, IDiagnosticsLogger 1 logger) at Microsoft.EntityFrameworkCore.Infrastructure.ModelValidator.Validate(IModel model, IDiagnosticsLogger 1 logger) at Microsoft.EntityFrameworkCore.Infrastructure.RelationalModelValidator.Validate(IModel model, IDiagnosticsLogger 1 logger) at Microsoft.EntityFrameworkCore.SqlServer.Internal.SqlServerModelValidator.Validate(IModel model, IDiagnosticsLogger 1 logger) at Microsoft.EntityFrameworkCore.Metadata.Conventions.ValidatingConvention.ProcessModelFinalized(IModel model) at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.ConventionDispatcher.ImmediateConventionScope.OnModelFinalized(IModel model) at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.ConventionDispatcher.OnModelFinalized(IModel model) at Microsoft.EntityFrameworkCore.Metadata.Internal.Model.FinalizeModel() at Microsoft.EntityFrameworkCore.ModelBuilder.FinalizeModel() at Microsoft.EntityFrameworkCore.Infrastructure.ModelSource.CreateModel(DbContext context, IConventionSetBuilder conventionSetBuilder, ModelDependencies modelDependencies) at Microsoft.EntityFrameworkCore.Infrastructure.ModelSource.GetModel(DbContext context, IConventionSetBuilder conventionSetBuilder, ModelDependencies modelDependencies) at Microsoft.EntityFrameworkCore.Internal.DbContextServices.CreateModel() at Microsoft.EntityFrameworkCore.Internal.DbContextServices.get_Model() at Microsoft.EntityFrameworkCore.Infrastructure.EntityFrameworkServicesBuilder.<>c.<TryAddCoreServices>b__7_3(IServiceProvider p) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactory(FactoryCallSite factoryCallSite, RuntimeResolverContext context) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor 1 logger) at Microsoft.EntityFrameworkCore.Metadata.Conventions.ValidatingConvention.ProcessModelFinalized(IModel model) at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.ConventionDispatcher.ImmediateConventionScope.OnModelFinalized(IModel model) at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.ConventionDispatcher.OnModelFinalized(IModel model) at Microsoft.EntityFrameworkCore.Metadata.Internal.Model.FinalizeModel() at Microsoft.EntityFrameworkCore.ModelBuilder.FinalizeModel() at Microsoft.EntityFrameworkCore.Infrastructure.ModelSource.CreateModel(DbContext context, IConventionSetBuilder conventionSetBuilder, ModelDependencies modelDependencies) at Microsoft.EntityFrameworkCore.Infrastructure.ModelSource.GetModel(DbContext context, IConventionSetBuilder conventionSetBuilder, ModelDependencies modelDependencies) at Microsoft.EntityFrameworkCore.Internal.DbContextServices.CreateModel() at Microsoft.EntityFrameworkCore.Internal.DbContextServices.get_Model() at Microsoft.EntityFrameworkCore.Infrastructure.EntityFrameworkServicesBuilder.<>c.<TryAddCoreServices>b__7_3(IServiceProvider p) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactory(FactoryCallSite factoryCallSite, RuntimeResolverContext context) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor 1 logger) at Microsoft.EntityFrameworkCore.Metadata.Conventions.ValidatingConvention.ProcessModelFinalized(IModel model) at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.ConventionDispatcher.ImmediateConventionScope.OnModelFinalized(IModel model) at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.ConventionDispatcher.OnModelFinalized(IModel model) at Microsoft.EntityFrameworkCore.Metadata.Internal.Model.FinalizeModel() at Microsoft.EntityFrameworkCore.ModelBuilder.FinalizeModel() at Microsoft.EntityFrameworkCore.Infrastructure.ModelSource.CreateModel(DbContext context, IConventionSetBuilder conventionSetBuilder, ModelDependencies modelDependencies) at Microsoft.EntityFrameworkCore.Infrastructure.ModelSource.GetModel(DbContext context, IConventionSetBuilder conventionSetBuilder, ModelDependencies modelDependencies) at Microsoft.EntityFrameworkCore.Internal.DbContextServices.CreateModel() at Microsoft.EntityFrameworkCore.Internal.DbContextServices.get_Model() at Microsoft.EntityFrameworkCore.Infrastructure.EntityFrameworkServicesBuilder.<>c.<TryAddCoreServices>b__7_3(IServiceProvider p) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactory(FactoryCallSite factoryCallSite, RuntimeResolverContext context) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor 2.VisitCallSiteMain(ServiceCallSite callSite, TArgument argument) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitCache(ServiceCallSite callSite, RuntimeResolverContext context, ServiceProviderEngineScope serviceProviderEngine, RuntimeResolverLock lockType) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScopeCache(ServiceCallSite singletonCallSite, RuntimeResolverContext context) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor 2.VisitCallSite(ServiceCallSite callSite, TArgument argument) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitConstructor(ConstructorCallSite constructorCallSite, RuntimeResolverContext context) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor 2.VisitCallSite(ServiceCallSite callSite, TArgument argument) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitConstructor(ConstructorCallSite constructorCallSite, RuntimeResolverContext context) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor 2.VisitCallSiteMain(ServiceCallSite callSite, TArgument argument) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitCache(ServiceCallSite callSite, RuntimeResolverContext context, ServiceProviderEngineScope serviceProviderEngine, RuntimeResolverLock lockType) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScopeCache(ServiceCallSite singletonCallSite, RuntimeResolverContext context) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor 2.VisitCallSite(ServiceCallSite callSite, TArgument argument) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.Resolve(ServiceCallSite callSite, ServiceProviderEngineScope scope) at Microsoft.Extensions.DependencyInjection.ServiceLookup.DynamicServiceProviderEngine.<>c__DisplayClass1_0.<RealizeService>b__0(ServiceProviderEngineScope scope) at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngine.GetService(Type serviceType, ServiceProviderEngineScope serviceProviderEngineScope) at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngineScope.GetService(Type serviceType) at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider provider, Type serviceType) at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService[T](IServiceProvider provider) at Microsoft.EntityFrameworkCore.DbContext.get_DbContextDependencies() at Microsoft.EntityFrameworkCore.DbContext.get_InternalServiceProvider() at Microsoft.EntityFrameworkCore.DbContext.Microsoft.EntityFrameworkCore.Infrastructure.IInfrastructure<System.IServiceProvider>.get_Instance() at Microsoft.EntityFrameworkCore.Infrastructure.Internal.InfrastructureExtensions.GetService[TService](IInfrastructure 2.VisitCallSite(ServiceCallSite callSite, TArgument argument) at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.Resolve(ServiceCallSite callSite, ServiceProviderEngineScope scope) at Microsoft.Extensions.DependencyInjection.ServiceLookup.DynamicServiceProviderEngine.<>c__DisplayClass1_0.<RealizeService>b__0(ServiceProviderEngineScope scope) at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngine.GetService(Type serviceType, ServiceProviderEngineScope serviceProviderEngineScope) at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngineScope.GetService(Type serviceType) at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider provider, Type serviceType) at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService[T](IServiceProvider provider) at Microsoft.EntityFrameworkCore.DbContext.get_DbContextDependencies() at Microsoft.EntityFrameworkCore.DbContext.get_InternalServiceProvider() at Microsoft.EntityFrameworkCore.DbContext.Microsoft.EntityFrameworkCore.Infrastructure.IInfrastructure<System.IServiceProvider>.get_Instance() at Microsoft.EntityFrameworkCore.Infrastructure.Internal.InfrastructureExtensions.GetService[TService](IInfrastructure 1 accessor) at Microsoft.EntityFrameworkCore.Infrastructure.AccessorExtensions.GetService[TService](IInfrastructure`1 accessor) at Microsoft.EntityFrameworkCore.Infrastructure.DatabaseFacade.get_Dependencies() at Microsoft.EntityFrameworkCore.Infrastructure.DatabaseFacade.EnsureCreated() at ProjectTest1.Program.Main(String[] args) in C:\Users\yamab\Desktop\ProjectTest1\ProjectTest1\Program.cs:line 48

Reading this tutorial I think I should do something like this

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Entity<User>()
                .Map<Studentt>(m => m.Requires("User").HasValue("S"))
                .Map<Teacher>(m => m.Requires("Usre").HasValue("T"));
}

Not sure this is what I should do nor how to do it exactly?

Answer 1

Thank you to @Fildor for the assistance and pointing me to Entity type hierarchy mapping

The solution was to add

public DbSet<Student> Students { get; set; }
public DbSet<Teacher> Teachers { get; set; }

Complet code:

using System;
using Microsoft.EntityFrameworkCore;
using System.ComponentModel.DataAnnotations;
using Microsoft.Extensions.Logging;

namespace ProjectTest1 {

    public abstract class User {
        [Key]
        public string FirstName { get; set; }

        public string LastName { get; set; }

        public string Password { get; set; }

        public string Email { get; set; }

        public bool IsAdmin { get; set; }

    }

    public class Student : User {
        public string Number { get; set; }
    }

    public class Teacher : User {
        public int Salary { get; set; }
    }

    public class Model : DbContext {

        public static readonly ILoggerFactory _loggerFactory = LoggerFactory.Create(builder => {
            builder.AddConsole();
        });
        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder) {
            base.OnConfiguring(optionsBuilder);
            optionsBuilder.UseSqlServer(@"Server=(localdb)\mssqllocaldb;Database=project")
                .EnableSensitiveDataLogging()
                .UseLoggerFactory(_loggerFactory);
        }

        public DbSet<User> Users { get; set; }
        public DbSet<Student> Students { get; set; }
        public DbSet<Teacher> Teachers { get; set; }
    }

    class Program {
        static void Main(string[] args) {
            using var model = new Model();
            model.Database.EnsureCreated();

            model.Users.RemoveRange(model.Users);
            model.SaveChanges();

            var guillaume = new Student() {
                FirstName = "guillaume", LastName = "b", Password = "azerty",
                Email = "guillaume@gmail.com", IsAdmin = true , Number = "150200"
            };
            var donald = new Teacher() {
                FirstName = "donald", LastName = "c", Password = "azerty",
                Email = "donald@gmail.com", IsAdmin = false, Salary = 35000
            };

            model.Users.AddRange(new User[] { guillaume, donald });
            model.SaveChanges();

        }
    }
}