EF core 5.0 doesn't detect change to DateTimeOffset's offset

[clement911]

I see the following bug with EF 5.0

var entity = dbCtx.Find<MyEntity>(123);//Load from DB context
entity.MyDateTimeOffset = entity.MyDateTimeOffset.ToOffset(entity.MyDateTimeOffset.Add(TimeSpan.FromHours(2)));//Switch the offset by 2 hours
ctx.Entry(order).State; //Return Unchanged but expecting Modified

I believe this happens because IEquatable<DateTimeOffset> considers that two DateTimeOffsets are equal if they represent the same absolute time.
However, from a DB perspective, the code above should detect the change and persist the new offset in the column (which is of type datetimeoffset in Sql Azure)

[dengere]

I can't reproduce it,
it could be something missed. entity.MyDateTimeOffset.Add(TimeSpan.FromHours(2)) produce new DateTimeOffset object. ToOffset acccept only TimeSpan, and it can not convert from DateTimeOffset to TimeSpan.

[clement911]

Here is a more comprehensive repro, using the InMemoryDatabase provider.

Program.cs

using Microsoft.EntityFrameworkCore;
using System;
using System.ComponentModel.DataAnnotations;

namespace ReproEFOffset
{
    public class MyEntity
    {
        [Key]
        public int Id { get; set; }

        public DateTimeOffset UpdatedAt { get; set; }
    }

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

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            base.OnConfiguring(optionsBuilder);
            optionsBuilder.UseInMemoryDatabase("MyDb");
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            var ctx = new MyContext();
            var entity = new MyEntity { Id = 1, UpdatedAt = DateTimeOffset.UtcNow };
            ctx.Add(entity);
            ctx.SaveChanges();

            entity.UpdatedAt = entity.UpdatedAt.ToOffset(TimeSpan.FromHours(-6));
            var entityState = ctx.Entry(entity).State;
            Console.WriteLine(entityState);//Displays Unchanged but expecting Modified
        }
    }
}

.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net5.0</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.EntityFrameworkCore.InMemory" Version="5.0.4" />
  </ItemGroup>

</Project>

[roji]

I can confirm this repros - and as @clement911 wrote this is due to the equality behavior .NET defines for DateTimeOffset, which doesn't take timezone differences into account.

[clement911]

Thanks @roji , can this be prioritized for the next release?

[roji]

@clement911 I've submitted a fix for this. In the meantime you can set up your own value comparer with the right behavior as described in the docs:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Blog>().Property(b => b.DateTimeOffset)
        .Metadata
        .SetValueComparer(new ValueComparer<DateTimeOffset>(
            (dto1, dto2) => dto1 == dto2 && dto1.Offset == dto2.Offset,
            dto => dto.GetHashCode()));
}

[clement911]

Awesome. Thanks for the quick fix!