ComplexCollection bug on new record creation

[RuslanLatsina]

Bug description

Hi, everyone - I faced the issue probably related to #37026 and got the error related to ComplexCollection .

I use

Microsoft.EntityFrameworkCore                                          10.0.1
Npgsql.EntityFrameworkCore.PostgreSQL                                  10.0.0

Error

The complex entry at the original ordinal '0' for the collection 'Blog.NestedJson.Items' cannot be accessed as the containing entry is in the added state.'

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();


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

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        => optionsBuilder
            .UseNpgsql("<connection string>")
            .LogTo(Console.WriteLine, LogLevel.Information)
            .EnableSensitiveDataLogging();

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

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

10.0.1

Database provider

Npgsql.EntityFrameworkCore.PostgreSQL

Target framework

NET10

Operating system

No response

IDE

No response

[roji]

I'm unable to reproduce this. I pasted your exact code above into a project with Npgsql.EntityFrameworkCore.PostgreSQL 10.0.0 and Microsoft.EntityFrameworkCore 10.0.1, and it seems to run just fine. The logs show:

info: 12/14/2025 08:02:12.940 RelationalEventId.CommandExecuted[20101] (Microsoft.EntityFrameworkCore.Database.Command) 
      Executed DbCommand (18ms) [Parameters=[@p0='{"Item":{"Name":"foo"},"Items":[{"Name":"bar"},{"Name":"baz"}]}' (Nullable = false) (DbType = Object), @p1='Blog1' (Nullable = false)], CommandType='Text', CommandTimeout='30']
      INSERT INTO "Blogs" ("NestedJson", "Name")
      VALUES (@p0, @p1)
      RETURNING "Id";