Regression: LINQ Select with struct ComplexProperty + collection navigation throws InvalidOperationException

[AwkEng]

Bug description

I ran into a regression upgrading from EF Core 11 Preview 1 to Preview 2. In full transparency, I had Claude produce a minimal repro.

https://github.com/AwkEng/EfCoreComplexPropertyBug

Upgrading from EF Core 11.0.0-preview.1 to 11.0.0-preview.2 introduces a regression when a LINQ Select projection combines:

1. A collection navigation whose elements have a readonly record struct ComplexProperty projected via constructor
2. A struct ComplexProperty with nested struct ComplexProperties projected via constructor on the same entity

Either projection works individually. When combined in the same Select, EF Core throws:

InvalidOperationException: An expression of type 'Outer' cannot be used to initialize an array of type 'System.Object'

The stack trace points to ShaperProcessingExpressionVisitor.ProcessProjection calling LiftComplexTypeToNewArray, which appears new in preview.2 and does not box the struct before adding it to the object[] array initializer expression.

Reproduces on both SQLite and PostgreSQL — this is an EF Core core issue, not provider-specific.

Your code

#:package Microsoft.EntityFrameworkCore@11.0.0-preview.2.26159.112
#:package Microsoft.EntityFrameworkCore.Sqlite@11.0.0-preview.2.26159.112

using Microsoft.EntityFrameworkCore;

var options = new DbContextOptionsBuilder<AppDbContext>()
    .UseSqlite("Data Source=:memory:")
    .Options;

using var db = new AppDbContext(options);
db.Database.OpenConnection();
db.Database.EnsureCreated();

var parentId = Guid.NewGuid();
db.Parents.Add(new Parent
{
    Id = parentId,
    Name = "P1",
    Coords = new Outer
    {
        First = new Inner { A = "1", B = "2" },
        Second = new Inner { A = "3", B = "4" }
    },
    Children = [new Child { Id = Guid.NewGuid(), ParentId = parentId, Data = new Inner { A = "x", B = "y" } }]
});
db.SaveChanges();

// Works in preview.1, throws in preview.2
var result = await db.Parents
    .AsNoTracking()
    .Where(p => p.Id == parentId)
    .Select(p => new ParentVm(
        p.Name,
        p.Children.Select(c => new ChildVm(new InnerVm(c.Data))).ToList(),  // collection nav + struct
        new OuterVm(p.Coords)                                               // nested struct
    ))
    .FirstOrDefaultAsync();

Console.WriteLine(result);

// ── Domain ──────────────────────────────────────────────────────────

public readonly record struct Inner
{
    public string? A { get; init; }
    public string? B { get; init; }
}

public readonly record struct Outer
{
    public Inner First { get; init; }
    public Inner Second { get; init; }
}

public class Child
{
    public Guid Id { get; set; }
    public Guid ParentId { get; set; }
    public Inner Data { get; set; }
    public Parent? Parent { get; set; }
}

public class Parent
{
    public Guid Id { get; set; }
    public string Name { get; set; } = default!;
    public Outer Coords { get; set; }
    public List<Child> Children { get; set; } = [];
}

// ── View models ─────────────────────────────────────────────────────

public record InnerVm(string? A, string? B)
{
    public InnerVm(Inner i) : this(i.A, i.B) { }
}

public record OuterVm(InnerVm First, InnerVm Second)
{
    public OuterVm(Outer o) : this(new InnerVm(o.First), new InnerVm(o.Second)) { }
}

public record ChildVm(InnerVm Data);
public record ParentVm(string Name, List<ChildVm> Children, OuterVm Coords);

// ── DbContext ───────────────────────────────────────────────────────

public class AppDbContext(DbContextOptions<AppDbContext> options) : DbContext(options)
{
    public DbSet<Parent> Parents => Set<Parent>();
    public DbSet<Child> Children => Set<Child>();

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Parent>(e =>
        {
            e.HasKey(x => x.Id);
            e.ComplexProperty(x => x.Coords, c =>
            {
                c.ComplexProperty(x => x.First, f =>
                {
                    f.Property(x => x.A).HasColumnName("first_a");
                    f.Property(x => x.B).HasColumnName("first_b");
                });
                c.ComplexProperty(x => x.Second, s =>
                {
                    s.Property(x => x.A).HasColumnName("second_a");
                    s.Property(x => x.B).HasColumnName("second_b");
                });
            });
            e.HasMany(x => x.Children).WithOne(x => x.Parent).HasForeignKey(x => x.ParentId);
        });

        modelBuilder.Entity<Child>(e =>
        {
            e.HasKey(x => x.Id);
            e.ComplexProperty(x => x.Data, d =>
            {
                d.Property(x => x.A).HasColumnName("data_a");
                d.Property(x => x.B).HasColumnName("data_b");
            });
        });
    }
}

Stack traces

System.InvalidOperationException: An expression of type 'Outer' cannot be used to initialize an array of type 'System.Object'
   at System.Linq.Expressions.Expression.NewArrayInit(Type type, IEnumerable`1 initializers)
   at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.<ProcessProjection>g__LiftComplexTypeToNewArray|19_1(Expression expression, Type newArrayType)
   at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.ProcessProjection(Expression expression)
   at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
   at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.ProcessProjection(Expression expression)
   at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.VisitExtension(Expression extensionExpression)
   at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.ProcessShaper(Expression shaperExpression, RelationalCommandCache& relationalCommandCache, IReadOnlyList`1& readerColumns, LambdaExpression& relatedDataLoaders, Int32& collectionId)
   at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.VisitShapedQuery(ShapedQueryExpression shapedQueryExpression)
   at Microsoft.EntityFrameworkCore.Query.ShapedQueryCompilingExpressionVisitor.VisitExtension(Expression extensionExpression)
   at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.VisitExtension(Expression extensionExpression)
   at Microsoft.EntityFrameworkCore.Query.QueryCompilationContext.CreateQueryExecutor[TResult](Expression query)
   at Microsoft.EntityFrameworkCore.Storage.Database.CompileQuery[TResult](Expression query, Boolean async)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.CompileQueryCore[TResult](IDatabase database, Expression query, IModel model, Boolean async)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.<>c__DisplayClass11_0`1.<ExecuteAsync>b__0()
   at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQuery[TResult](Object cacheKey, Func`1 compiler)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.ExecuteAsync[TResult](Expression query, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.ExecuteAsync[TResult](Expression expression, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.ExecuteAsync[TSource,TResult](MethodInfo operatorMethodInfo, IQueryable`1 source, Expression expression, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.ExecuteAsync[TSource,TResult](MethodInfo operatorMethodInfo, IQueryable`1 source, Expression expression, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.FirstOrDefaultAsync[TSource](IQueryable`1 source, CancellationToken cancellationToken)

Verbose output

EF Core version

11.0.0-preview.2.26159.112 (regression from 11.0.0-preview.1.26104.118)

Database provider

Microsoft.EntityFrameworkCore.Sqlite 11.0.0-preview.2 + Npgsql.EntityFrameworkCore.PostgreSQL 11.0.0-preview.2

Target framework

.NET 11.0

Operating system

Windows 11

IDE

Visual Studio 2022

[roji]

AI Analysis

Bug confirmed ✅

The reported bug is confirmed. A LINQ Select projection that combines a struct complex property with a collection navigation throws:

System.InvalidOperationException: An expression of type 'MyStruct' cannot be used to initialize an array of type 'System.Object'

The root cause is a missing boxing conversion when a value-type (struct) complex property is placed into an object[] array during shaper processing. Class complex types work fine — this is specific to struct complex types.

Regression confirmed ✅

The user reported this as a regression from EF Core 11.0.0-preview.1 to 11.0.0-preview.2. This is confirmed:

Version	Result
EF Core 9.0.13	✅ Works
EF Core 10.0.0 – 10.0.3	✅ Works
EF Core 11.0.0-preview.1	✅ Works
EF Core 11.0.0-preview.2	❌ Fails

The regression was introduced between 11.0.0-preview.1 and 11.0.0-preview.2.

Regressing commit

The regression was introduced by commit 0555efa8a — "Fix projecting complex type in ProjectionBinder (#37552)", which fixed #37551.

That commit changed RelationalProjectionBindingExpressionVisitor to handle complex types as RelationalStructuralTypeShaperExpression (via base.Visit(shaper)) instead of failing to translate them. This new code path causes the complex type to flow through CompensateForCollectionMaterialization in ShaperProcessingExpressionVisitor, which adds the expression to _valuesArrayInitializers without boxing:

Expression CompensateForCollectionMaterialization(ParameterExpression parameter, Type resultType)
{
    if (_containsCollectionMaterialization)
    {
        _valuesArrayInitializers!.Add(parameter);  // ← BUG: no boxing for value types
        ...
    }
}

This contrasts with the scalar projection binding path (around line 855), which correctly boxes:

if (expressionToAdd.Type.IsValueType)
{
    expressionToAdd = Convert(expressionToAdd, typeof(object));
}

When the _valuesArrayInitializers list is later used in NewArrayInit(typeof(object), _valuesArrayInitializers), the runtime throws because a struct expression can't be stored in an object[] without an explicit Convert (boxing).

Fix: CompensateForCollectionMaterialization should box value types before adding them to _valuesArrayInitializers, similar to the scalar path.

Provider

Reproduced on both SQL Server and SQLite. This is a core EF Core issue (query compilation), not provider-specific.

Minimal repro

The repro is in Program.cs. Key conditions to trigger the bug:

1. An entity with a struct (value type) complex property
2. The same entity has a collection navigation
3. A Select projection that includes both the struct complex property and the collection navigation

Note: if the complex type is a class instead of a struct, the bug does not occur.

Possible duplicates

No duplicate issues found in the EF Core repository. The bug was introduced by the fix for #37551.

Repro code

Minimal repro

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging;

await using var db = new AppDbContext();
await db.Database.EnsureDeletedAsync();
await db.Database.EnsureCreatedAsync();

var result = await db.Parents
    .Select(p => new
    {
        Children = p.Children.Select(c => c.Id).ToList(),
        p.Data
    })
    .FirstOrDefaultAsync();

Console.WriteLine(result);

public readonly record struct MyStruct
{
    public string? A { get; init; }
}

public class Child
{
    public Guid Id { get; set; }
    public Guid ParentId { get; set; }
    public Parent? Parent { get; set; }
}

public class Parent
{
    public Guid Id { get; set; }
    public MyStruct Data { get; set; }
    public List<Child> Children { get; set; } = [];
}

public class AppDbContext : DbContext
{
    public DbSet<Parent> Parents => Set<Parent>();

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        => optionsBuilder
            .UseSqlServer(Environment.GetEnvironmentVariable("Test__SqlServer__DefaultConnection"))
            .LogTo(Console.WriteLine, LogLevel.Information)
            .EnableSensitiveDataLogging();

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Parent>(e =>
        {
            e.ComplexProperty(x => x.Data);
            e.HasMany(x => x.Children).WithOne(x => x.Parent).HasForeignKey(x => x.ParentId);
        });
    }
}

Stack trace

System.InvalidOperationException: An expression of type 'MyStruct' cannot be used to initialize an array of type 'System.Object'
   at System.Linq.Expressions.Expression.NewArrayInit(Type type, IEnumerable`1 initializers)
   at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.ProcessShaper(...)
   at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.VisitShapedQuery(...)
   ...