Fix ArgumentOutOfRangeException when deleting from ComplexCollection with nested collections

[Copilot]

Description
When deleting an item from a ComplexCollection that contains nested arrays or lists, an ArgumentOutOfRangeException is thrown during SaveChanges in the AcceptChanges phase. The database update succeeds, but the exception prevents normal completion of the operation.

Customer impact
Customers cannot delete items from complex collections that contain nested collections/arrays using patterns like entity.Collection = [.. entity.Collection.Where(predicate)] without encountering an exception. While the database is updated correctly, the exception disrupts the application flow and prevents proper error handling.

Workaround: Use RemoveAt() or Clear() methods instead of reassigning the collection with filtered results, or enable the old behavior with AppContext.SetSwitch("Microsoft.EntityFrameworkCore.Issue37585", true).

How found
Customer reported (issue #37585). At least one customer is affected based on the report and reactions (7 👍, 1 👀).

Regression
This appears to be a regression in EF Core 10.0.2.

Testing

• Added Remove_element_from_complex_collection_using_Where_with_nested_array test that reproduces the exact scenario
• All 20 ComplexCollectionJsonUpdate tests pass
• All 23 InternalComplexEntry tests pass
• Verified the fix handles the edge case of invalid ordinals during state transitions
• Added quirk mode switch to allow reverting to old behavior if needed

Risk
Low. The changes are surgical and only affect reading collection counts when the containing entry has invalid ordinals:

• Checks if containing entry is a complex entry with ordinal < 0 before reading from CLR
• Falls back to entries list count (source of truth) when ordinal is invalid
• Normal behavior preserved - CLR collection is read when ordinals are valid
• Quirk mode switch (Microsoft.EntityFrameworkCore.Issue37585) allows customers to use old behavior during migration
• All existing tests pass, confirming no regression in normal scenarios

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Deleting an item from a ComplexCollection, that contains an array results in Error</issue_title>
<issue_description>### Bug description

This may be resolved with the same fix as #37377; however, posting to be sure.

When deleting an item from a ComplexCollection, that Contains an array, an error is thrown.

Using the code below, calling SaveChanges(), results in an exception. What is unusual, is the save still goes through and the database result is correct.

Your code

#:package Microsoft.EntityFrameworkCore@10.0.2
#:package Npgsql.EntityFrameworkCore.PostgreSQL@10.0.0
#:package Testcontainers@4.10.0

using DotNet.Testcontainers.Builders;
using DotNet.Testcontainers.Containers;
using EfCore10Regression.Tests;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging;
using Npgsql;
using static EfCore10Regression.Tests.Models;

var fixture = new PostgresContainerFixture();
await fixture.InitializeAsync();
Console.WriteLine($"Postgres started. ConnectionString={fixture.ConnectionString}");
Console.WriteLine($"Logging SQL to: {fixture.LogFilePath}");

await using (var ctx = fixture.CreateContext())
{
    var modelBs = new List<ModelB>
    {
        new() {
            Id = 1,
            ModelCs = []
        }
    };

    ctx.Models.Add(new ModelA
    {
        Id = 0,
        ModelBs = modelBs
    });

    await ctx.SaveChangesAsync();
}

await using var context = fixture.CreateContext();

var rawData = await context.Models.SingleAsync();
Console.WriteLine($"Nbr items before {rawData.ModelBs.Count}");

rawData.ModelBs = [.. rawData.ModelBs.Where(x => x.Id != 1)];
Console.WriteLine($"Nbr items after {rawData.ModelBs.Count}");

await context.SaveChangesAsync();
Console.WriteLine("SUCCESS!!");
Console.ReadLine();

await fixture.DisposeAsync();

namespace EfCore10Regression.Tests
{
    public class RegressionDbContext(DbContextOptions<RegressionDbContext> options) : DbContext(options)
    {
        public DbSet<Models.ModelA> Models => Set<Models.ModelA>();

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Models.ModelA>(b => b.ComplexCollection(c => c.ModelBs, c =>
            {
                c.ToJson();
            }));
        }
    }

    public static class Models
    {
        public class ModelA
        {
            public int Id { get; set; }
            public List<ModelB> ModelBs { get; set; } = [];
        }

        public class ModelB
        {
            public int Id { get; set; }
            public List<ModelC> ModelCs { get; set; } = [];
        }

        public record ModelC
        {
            public Guid Id { get; set; }
        }
    }

    public class PostgresContainerFixture : IAsyncLifetime
    {
        private readonly IContainer _pgContainer;
        private StreamWriter? _logWriter;
        public string ConnectionString { get; private set; } = string.Empty;
        public string? LogFilePath { get; private set; }

        public PostgresContainerFixture()
        {
            _pgContainer = new ContainerBuilder("postgis/postgis:latest")
                .WithPortBinding(5432, assignRandomHostPort: true)
                .WithEnvironment("POSTGRES_PASSWORD", "postgres")
                .WithEnvironment("POSTGRES_USER", "postgres")
                .WithEnvironment("POSTGRES_DB", "testdb")
                .WithWaitStrategy(Wait.ForUnixContainer().UntilInternalTcpPortIsAvailable(5432))
                .Build();
        }

        public async Task InitializeAsync()
        {
            await _pgContainer.StartAsync();
            var host = _pgContainer.Hostname;
            var port = _pgContainer.GetMappedPublicPort(5432);
            ConnectionString = new NpgsqlConnectionStringBuilder
            {
                Host = host,
                Port = port,
                Username = "postgres",
                Password = "postgres",
                Database = "testdb"
            }.ToString();

            LogFilePath = Path.Combine(Path.GetTempPath(), $"efcore-sql-{Guid.NewGuid():N}.log");
            _logWriter = new StreamWriter(File.Open(LogFilePath, FileMode.Create, FileAccess.Write, FileShare.Read))
            {
                AutoFlush = true
            };
        }

        public async Task DisposeAsync()
        {
            await _pgContainer.StopAsync();
            await _pgContainer.DisposeAsync();
            _logWriter?.Dispose();
        }

        public RegressionDbContext CreateContext()
        {
            var optionsBuilder = new DbContextOptionsBuilder<RegressionDbContext>()
                .UseNpgsql(ConnectionString, a => a.UseNetTopologySuite())
                .EnableSensitiveDataLogging()
                .EnableDetailedErrors();

            if (_logWriter is not null)
            {
                optionsBuilder.LogTo(_logW...

</details>



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- Fixes dotnet/efcore#37585

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[AndriySvyryd]

@copilot Several tests are failing. Make sure to run all tests after fixing these:
Complex_collection_detects_moved_null_elements_and_replaced_instances_as_unchanged

Assert.Equal() Failure: Collections differ
                                                                           ↓ (pos 1)
Expected: <generated>                                           [Modified, Unchanged, Added]
Actual:   ListSelectIterator<InternalComplexEntry, EntityState> [Modified, Modified, Added]
                                                                           ↑ (pos 1)

[Copilot]

@copilot Several tests are failing. Make sure to run all tests after fixing these:
Complex_collection_detects_moved_null_elements_and_replaced_instances_as_unchanged

...

Fixed in 704c6a1. The issue was that SetState is called during change detection (not just after AcceptChanges), so we need to read from the CLR collection to detect size changes. The fix now uses exception handling as a fallback only when ordinals are out of bounds, preserving normal change detection behavior.

[AndriySvyryd]

@copilot Update progress by rewriting the PR summary using this template:

Fixes #{number}

**Description**
{Issue description}

**Customer impact**
{How does the reported issue affects customer's app? Are there workarounds?}

**How found**
{Was it customer reported or found during verification? How many customers are affected?}

**Regression**
{Is it a regression from a released version? Which one?}

**Testing**
{How the changes were tested}

**Risk**
{Low/Medium/High, argument why}

[Copilot]

@copilot Update progress by rewriting the PR summary using this template:

...

Updated the PR description with the requested template format.