@wilfriedb can you share the listing of the unit test that is failing (or other form of full repro of this issue)?

I'm trying the following:

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

        var e1 = new MyEntity { Id = 1, Do = new DateOnly(2000, 1, 1), Ndo = new DateOnly(2024, 2, 2) };
        var e2 = new MyEntity { Id = 2, Do = new DateOnly(2001, 1, 1), Ndo = null };

        ctx.MyEntities.AddRange(e1, e2);
        await ctx.SaveChangesAsync();


        var q = await ctx.MyEntities.Select(x => x.Ndo.ToString()).ToListAsync();
        var q2 = await ctx.MyEntities.Where(x => x.Ndo.ToString() != "foo").ToListAsync();
    }

    public class MyContext : DbContext
    {
        public DbSet<MyEntity> MyEntities { get; set; }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
        }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder
                    .UseInMemoryDatabase("myDateOnlyDb")
                    .LogTo(Console.WriteLine, LogLevel.Information)
                    .EnableSensitiveDataLogging();
        }
    }

    public class MyEntity
    {
        public int Id { get; set; }
        public DateOnly Do { get; set; }
        public DateOnly? Ndo { get; set; }
    }

and it works fine.

Expression tree we create here is

new QueryingEnumerable<string>(
    queryContext, 
    InMemoryShapedQueryCompilingExpressionVisitor.Table(
        queryContext: queryContext, 
        entityType: EntityType: MyEntity)
        .Select(valueBuffer => new ValueBuffer(new object[]{ ExpressionExtensions.ValueBufferTryReadValue<DateOnly?>(
            valueBuffer: valueBuffer, 
            index: 2, 
            property: Property: MyEntity.Ndo (DateOnly?)).ToString() })) // <- ToString() on Nullable<DateOnly>
        .Select(valueBuffer => new ValueBuffer(new object[]{ ExpressionExtensions.ValueBufferTryReadValue<string>(
            valueBuffer: valueBuffer, 
            index: 0, 
            property: null) })), 
    Func<QueryContext, ValueBuffer, string>, 
    AdHocMiscellaneousQueryInMemoryTest+MyContext, 
    False, 
    True
)

which is has no problems calling ToString method on DateOnly? argument.

Hello @maumar, I'm in the process of making a minimal repo that will reproduce the issue. There are many, many expressions in this code therefore this process is not going fast . When I've finished this I will post an update here.

Hello @maumar here is a minimal repo that reproduces the issue: https://github.com/wilfriedb/EFCoreReproduce

In this repo, the unit test will fail with an exception, as mentioned above.
When downgraded to EF Core 8, the test will succeed.

Also, with a minimal change in the file MapperProfile.cs, as indicated in the comments, the test will succeed.

Fun fact, the DateOnly field ValueDate on the PaymentModel class, on which the exception occurs, is not nullable. But when debugging in the file InMemoryExpressionTranslatingExpressionVisitor, the field (in an expression) is promoted (demoted?) to a nullable DateOnly. This is also the case in EF Core 8, but on line 888, in EF Core 9 the if statement is skipped (the condition evaluates to false), but in EF Core 8 the if statement is entered (the condition evaluates to true).

I have the same issue, here is the 1 file repro https://github.com/domagojmedo/EfCore35299

You can just comment and uncomment line in .csproj

Shouldn't this at least be added to breaking changes for EF 9?

I ran into this, doesn't really understand how it could be fixed / worked around. Do we need to downgrade? Can i ran EF Core 8 with .net 9?

You can, that's what I did. Using [8.0.11] in test project

regression introduced in #33706
The way we receive the query, ToString method is defined on Int32, but as part of the process, the argument itself becomes nullable (as we are accessing optional entity. We have a code to mitigate that:

we add a null check and only if the object is not null, we convert the object to non-null, to match the type and call the method. Problem is that we don't do that for Nullable<>.ToString - the way that we check for it is by method name only, so we accidentally also filtered out non-nullable ToString. We should check the declaring type as well

workaround is to convert the argument to nullable before calling ToString():

                AuthorId = ((int?)x.Author!.Id).ToString()

Yes, but that means we have to write our EF code differently just because of tests and that's not something I'm very keen on doing. Think we're gonna stay on version 8 and hope it's fixed in 10