GroupBy aggregate over a required navigation with a query filter drops entire groups (Regression in 11.0) #38965

modelBuilder.Entity<Product>().HasQueryFilter(p => !p.Discontinued);

// 1 — Count alone
ctx.OrderDetails.GroupBy(od => od.OrderID)
    .Select(g => new { g.Key, Count = g.Count() })

// 2 — Count plus an aggregate that traverses Product
ctx.OrderDetails.GroupBy(od => od.OrderID)
    .Select(g => new { g.Key, Count = g.Count(), MaxStock = g.Max(x => (int?)x.Product.UnitsInStock) })

// 3 — the same question, traversal moved into the GroupBy element selector
ctx.OrderDetails.GroupBy(od => od.OrderID, od => new { od.Product.UnitsInStock, od.Quantity })
    .Select(g => new { g.Key, Count = g.Count(), MaxStock = g.Max(x => (int?)x.UnitsInStock) })

using Microsoft.EntityFrameworkCore;

using var ctx = new NorthwindContext();
ctx.Database.EnsureCreated();

ctx.AddRange(
    new Product { ProductID = 1, ProductName = "Chai", Discontinued = false, UnitsInStock = 39 },
    new Product { ProductID = 2, ProductName = "Mishi Kobe Niku", Discontinued = true, UnitsInStock = 29 },
    new Order { OrderID = 10248 },
    new Order { OrderID = 10249 },
    new OrderDetail { OrderID = 10248, ProductID = 1, Quantity = 12 },
    new OrderDetail { OrderID = 10249, ProductID = 2, Quantity = 9 });
ctx.SaveChanges();
ctx.ChangeTracker.Clear();

var q1 = ctx.OrderDetails.GroupBy(od => od.OrderID)
    .Select(g => new { g.Key, Count = g.Count() })
    .OrderBy(x => x.Key).ToList();

var q2 = ctx.OrderDetails.GroupBy(od => od.OrderID)
    .Select(g => new { g.Key, Count = g.Count(), MaxStock = g.Max(x => (int?)x.Product.UnitsInStock) })
    .OrderBy(x => x.Key).ToList();

var q3 = ctx.OrderDetails.GroupBy(od => od.OrderID, od => new { od.Product.UnitsInStock, od.Quantity })
    .Select(g => new { g.Key, Count = g.Count(), MaxStock = g.Max(x => (int?)x.UnitsInStock) })
    .OrderBy(x => x.Key).ToList();

Console.WriteLine($"1) {q1.Count} groups");   // 2
Console.WriteLine($"2) {q2.Count} groups");   // 1 on 11.0, 2 on 10.0
Console.WriteLine($"3) {q3.Count} groups");   // 2

public class Product
{
    public int ProductID { get; set; }
    public string ProductName { get; set; } = null!;
    public bool Discontinued { get; set; }
    public short UnitsInStock { get; set; }
}

public class Order
{
    public int OrderID { get; set; }
}

public class OrderDetail
{
    public int OrderID { get; set; }
    public int ProductID { get; set; }
    public short Quantity { get; set; }
    public Order Order { get; set; } = null!;
    public Product Product { get; set; } = null!;
}

public class NorthwindContext : DbContext
{
    private readonly Microsoft.Data.Sqlite.SqliteConnection _connection = new("DataSource=:memory:");

    public DbSet<Product> Products => Set<Product>();
    public DbSet<Order> Orders => Set<Order>();
    public DbSet<OrderDetail> OrderDetails => Set<OrderDetail>();

    public NorthwindContext() => _connection.Open();

    protected override void OnConfiguring(DbContextOptionsBuilder b)
        => b.UseSqlite(_connection);

    protected override void OnModelCreating(ModelBuilder mb)
    {
        mb.Entity<Product>().HasQueryFilter(p => !p.Discontinued);

        mb.Entity<OrderDetail>().HasKey(od => new { od.OrderID, od.ProductID });
        mb.Entity<OrderDetail>().HasOne(od => od.Order).WithMany().HasForeignKey(od => od.OrderID);
        mb.Entity<OrderDetail>().HasOne(od => od.Product).WithMany().HasForeignKey(od => od.ProductID);
    }

    public override void Dispose()
    {
        base.Dispose();
        _connection.Dispose();
    }
}