Issue with change tracker not detecting changes on nested complex collections

[mario-mestrovic]

Bug description

While making a workaround for this #37009 and until .NET 10 and EF Core 10 are GA I've found more issues.

Looks like EF can't detect changes in nested complex collections (like Items in this example) (which means SaveChanges won't trigger an UPDATE statement).

Your code

using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging;

await using var context = new BlogContext();
await context.Database.EnsureDeletedAsync();
await context.Database.EnsureCreatedAsync();

var blog = new Blog
{
    Name = "Blog1",
    NestedJson = new NestedJson
    {
        Item = new() { Name = "foo" },
        Items =
            [
                new() { Name = "bar" },
                new() { Name = "baz" },
            ]
    }
};
context.Blogs.Add(blog);
await context.SaveChangesAsync();


blog.NestedJson = blog.NestedJson with
{
    Items = [
                new() { Name = "bar" },
                new() { Name = "baz" },
                new() { Name = "new-bar" },
            ]
};


context.ChangeTracker.DetectChanges();

var modified = context.ChangeTracker.Entries().Any(x=>x.State == EntityState.Modified);
Console.WriteLine($"Is Modified: {modified}"); // Output: Is Modified: False (should be True)

public class BlogContext : DbContext
{
    public DbSet<Blog> Blogs { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        => optionsBuilder
            .UseSqlServer("Server=localhost;Database=test;User=SA;Password=Abcd5678;Connect Timeout=60;ConnectRetryCount=0;Encrypt=false")
            .LogTo(Console.WriteLine, LogLevel.Information)
            .EnableSensitiveDataLogging();

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Blog>().ComplexProperty(e => e.NestedJson, b =>
        {
            b.ToJson();

            b.ComplexProperty(a => a.Item, b =>
            {
                b.Property(x => x.Name).HasJsonPropertyName("name");
            });

            b.ComplexCollection(a => a.Items, b =>
            {
                b.Property(x => x.Name).HasJsonPropertyName("name");
            });
        });
    }
}

public class Blog
{
    public int Id { get; set; }
    public string Name { get; set; }

    public NestedJson NestedJson { get; set; }
}

public record NestedJson
{
    public NestedItem Item { get; init; }
    public List<NestedItem> Items { get; init; }
}

public record NestedItem
{
    public string Name { get; init; } = string.Empty;
}

Stack traces

Verbose output

EF Core version

10 RC2

Database provider

No response

Target framework

.NET 10 RC2

Operating system

Windows 11

IDE

Visual Studio 2026

[roji]

/cc @AndriySvyryd

[mario-mestrovic]

Any news on reproducing this? Should we expect a fix before 10.0 GA?

[roji]

@mario-mestrovic 10.0 GA is already completely locked down, and anything less than a critical showstopper won't make it in at this point (and this doesn't look like one).

[mario-mestrovic]

Hope it makes it into 10.0.x so we don't have to wait until 11.

Its def not critical but it's 'serious'.

[AndriySvyryd]

As a workaround, you can mark the nested entries as modified manually:

var nestedJson = context.Entry(blog).ComplexProperty(b => b.NestedJson);
var items = nestedJson.ComplexCollection(j => j.Items);

items[0].State =  EntityState.Modified;
items[1].State =  EntityState.Modified;
items[2].State =  EntityState.Added;

If you delete an item you can mark it like this:

items.GetOriginalEntry(1).State = EntityState.Deleted

[rlcarrierscsharp]

I'm confused... you all have tests that cover complex collections, how did this get missed? To clarify (that sounds like a jerk kind of question, but I am not meaning it in that way), I'm curious if there is something specific with the modification that is tripping up change detection?

[mario-mestrovic]

As a workaround, you can mark the nested entries as modified manually:

var nestedJson = context.Entry(blog).ComplexProperty(b => b.NestedJson);
var items = nestedJson.ComplexCollection(j => j.Items);

items[0].State = EntityState.Modified;
items[1].State = EntityState.Modified;
items[2].State = EntityState.Added;
If you delete an item you can mark it like this:

items.GetOriginalEntry(1).State = EntityState.Deleted

@AndriySvyryd I just tried and this doesn't work as described. You can't compile this line var items = nestedJson.ComplexCollection(j => j.Items); becasue j is of type Blog not NestedJson

The workaround is to mark the whole complex property as modified like this context.Entry(blog).ComplexProperty(b => b.NestedJson).IsModified = true and that's probably what's most practical as it's super impractical to actually detect what exactly changed inside the complex property