TPC returns incorrect items when using generic entities

[SpazeDev]

Bug description

When using TPC with generic entities EF is able to insert rows without a problem but unable to retrieve them correctly.

When running the code EF returns 4 entities of type ReproEntity<int> instead of the added, 2 ReproEntity<int> and 2 ReproEntity<string> entities.
Looking at the generated query shows that EF uses ReproEntity as the Discriminator for both types:

SELECT "r"."Id", "r"."Value", NULL AS "Value0", 'ReproEntity' AS "Discriminator"
FROM "ReproEntity<int>" AS "r"
UNION ALL
SELECT "r0"."Id", NULL AS "Value", "r0"."Value" AS "Value0", 'ReproEntity' AS "Discriminator"
FROM "ReproEntity<string>" AS "r0"

Your code

using System;
using System.Linq;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Diagnostics;

namespace Repro;

internal class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine("### Databse Setup");
        using (var dbContext = new ReproDbContext())
        {
            dbContext.Database.EnsureDeleted();
            dbContext.Database.EnsureCreated();

            dbContext.Set<BaseEntity>().AddRange([
                new ReproEntity<int>() { Id = 1, Value = 1 },
                new ReproEntity<int>() { Id = 2, Value = 2 },
                new ReproEntity<string>() { Id = 3, Value = "3" },
                new ReproEntity<string>() { Id = 4, Value = "4" },
            ]);
            dbContext.SaveChanges();
        }

        Console.WriteLine("### Select Query");
        using (var dbContext = new ReproDbContext())
        {
            var entities = dbContext.Set<BaseEntity>().ToList();

            foreach (var entity in entities)
            {
                Console.WriteLine($"{entity.Id} - {entity.GetType().FullName}");
            }
        }
    }
}

public class ReproDbContext : DbContext
{
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);

        modelBuilder.Entity<BaseEntity>()
            .UseTpcMappingStrategy()
            .HasKey(x => x.Id);

        modelBuilder.Entity<ReproEntity<int>>();
        modelBuilder.Entity<ReproEntity<string>>();
    }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder) => optionsBuilder
        .UseSqlite("Data Source=Repro.db")
        .LogTo(
            (e, l) => e.Id == RelationalEventId.CommandExecuting,
            e => Console.WriteLine(((CommandEventData)e).Command.CommandText));
}

public abstract class BaseEntity
{
    public int Id { get; set; }
}

public class ReproEntity<T> : BaseEntity
{
    public T Value { get; set; }
}

Stack traces

Verbose output

EF Core version

9.0.2

Database provider

Microsoft.EntityFrameworkCore.Sqlite

Target framework

net9.0

Operating system

Windows 10

IDE

Visual Studio 2022 17.12.4