Assignment to inherited field, bypassing an hiding field

[Alexcrazy42]

Question

Hello! I have a question about assignment to class hierarchy in EF Core.

This class inherited by simple class Entity, that just add generic Identifier to inheritor classes. I accidentally hide the field from the parent by redefinition without keyword new.

Then I fetch data with EF I have this:

That is, I have 2 fields: from parent and from class.

And then I make some updates EF take field from class (Guid.Empty):

In fluent configuration then I have hiding field, exactly this field detect as key.

Naturally, removing Id from inheritor solve this.
I thought it wasn't a bug.
But, I have question about how EF detect what field in hierarchy need to fill. Please, give me hints where the part is located with filling fields from the inheritance hierarchy.

Your code

Stack traces

Verbose output

EF Core version

9.0.0

Database provider

Npgsql.EntityFrameworkCore.PostgreSQL

Target framework

.NET 8.0

Operating system

Windows 11

IDE

Rider 2024

[maumar]

I'm unable to reproduce this. Please provide full standalone repro that shows the issue. When trying in my environment I'm seeing derived property being used both for update and for query.

Here is what I tried - you can modify this code in such a way that it reproduces the issue

    [ConditionalFact]
    public async Task Repro123()
    {
        using (var ctx = new MyContext())
        {
            await ctx.Database.EnsureDeletedAsync();
            await ctx.Database.EnsureCreatedAsync();

            var e = new UserSetting { Id = Guid.NewGuid(), Name = "foo" };
            ctx.Set<UserSetting>().Add(e);
            await ctx.SaveChangesAsync();
        }



        using (var ctx = new MyContext())
        {
            var result = await ctx.Set<UserSetting>().FirstAsync();

            result.Name = "bar";

            await ctx.SaveChangesAsync();
        }


        using (var ctx = new MyContext())
        {
            var result = await ctx.Set<UserSetting>().FirstAsync();
        }

    }

    public class MyContext : DbContext
    {
        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<UserSetting>().HasKey(x => x.Id);
        }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder
                .UseSqlServer(@"Server=(localdb)\mssqllocaldb;Database=Repro35643;Trusted_Connection=True;MultipleActiveResultSets=true")
                .EnableSensitiveDataLogging();
        }
    }

    public class Entity<T>
    {
        public T Id { get; set; }
    }

    public class UserSetting : Entity<Guid>
    {
        public new Guid Id { get; set; }
        public string Name { get; set; }
    }

[Alexcrazy42]

all you need to reproduce problem: delete new on this line in class UserSetting: public new Guid Id { get; set; }

line should be: public Guid Id { get; set; }

I understand, that it is a source of problem, but I want to understand why EF with this EntityConfiguration:
modelBuilder.Entity<UserSetting>().HasKey(x => x.Id);

perceive Id from inheritor, but then fetch data from DB, fill id from base class: