DbContext.ChangeTracker.HasChanges() not working as expected

[midicine]

We are not able to find any Added/Updated/Deleted entities from ChangeTracker.Entries(), but ChangeTracker.HasChanges() shows TRUE

Exception message: N/A
Stack trace: N/A

Steps to reproduce

using Microsoft.EntityFrameworkCore;
using System;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;

namespace TestEntityFrameworkCore
{
    public class Booking
    {
        public int Id { get; set; }
        public Status Status { get; set; }
    }

    public class Status
    {
        public string Value { get; set; }
    }

    public class SqlDbContext : DbContext
    {
        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
            => optionsBuilder
                .UseSqlServer(@"Server=.;Database=dbname;Trusted_Connection=True;");

        protected override void OnModelCreating(ModelBuilder builder)
        {
            builder.Entity<Booking>(m =>
            {
                m.ToTable("Booking", "dbo");
                m.HasKey(x => x.Id);
                m.OwnsOne(x => x.Status, nav =>
                {
                    nav.Property(x => x.Value)
                        .HasColumnName("Status");
                });
            });
        }
    }

    public class Program
    {
        public static async Task Main()
        {
            using (var context = new SqlDbContext())
            {
                var booking = await context.Set<Booking>()
                    .FirstOrDefaultAsync(x => x.Id == 1897229);
                booking.Status = new Status() { Value = "Cancelled" };
                context.Entry(booking).State = EntityState.Unchanged;
                context.Entry(booking.Status).State = EntityState.Unchanged;
                // we expect there are no changes in context.ChangeTracker()
                if (context.ChangeTracker.HasChanges())
                {
                    // but context.ChangeTracker shows there are changes(), and we found ChangedCount of StateManager in ChangeTracker had value "1"
                    var test = context.ChangeTracker.Entries().Where(x => x.State != EntityState.Unchanged).ToList();
                    Console.WriteLine(test.Count); // output 0
                }
                await context.SaveChangesAsync(); // and will not execute any db command here
            }
        }
    }
}

Further technical details

EF Core version: 2.2.2
Database Provider: Microsoft.EntityFrameworkCore.SqlServer
Operating system: Windows 10 Pro 1809
IDE: Visual Studio 2017 15.9.7

[ajcvickers]

Note for triage: I was able to reproduce this.

[ajcvickers]

@AndriySvyryd The issue here is that we create a special additional entry to handle owned type replacement--this is the state manager contents when HasChanges is called:

Booking {Id: 1} Unchanged
  Id: 1 PK
  Status: {BookingId: 1}
Status (Shared) {BookingId: 1} Deleted
  BookingId: 1 PK FK
  Value: 'S'
Status (Shared) {BookingId: 1} Unchanged
  BookingId: 1 PK FK
  Value: 'Cancelled'

So it's clear why HasChanges returns true. But if HasChanges is intended to indicate whether or not changes need to be made to the database, then this is wrong.

On the other hand, if HasChanges is intended to only indicate that there might be changes made to the database, then this is okay. Although HasChanges is then less useful.

Thoughts?

[AndriySvyryd]

The way it's described I think it should return false. If you want to detect this case you'd need to use different API.

[AndriySvyryd]

But perhaps the way to fix this is that setting the state to unchanged should detach the deleted shared entry and copy over the original values.