EF Core 8 & 9 throw when "external" sets of primitive types are included in select

[ravindUwU]

Bug description

I also noticed that when a variable that is a HashSet<int> (for example) is included in the select expression, EF Core 8 & 9 throw errors that seem to be JSON-serialization related. Like in #35567, this issue doesn't seem to occur when a non-primitive variable is included in the select expression.

Please refer to the reproduction and the stack trace included below 🙂.

• EF core 7.0.20 runs the queries with no errors.

  

• EF core 8.0.12 & 9.0.1 throw as described.

  

Your code

public class Program
{
	public static async Task Main()
	{
		var db = new Db();
		var listOfInt = new List<int> { 1 };
		var setOfDouble = new HashSet<double> { 1d };
		var anObject = new { };

		Write($"EF Core {typeof(DbContext).Assembly.GetName().Version}");

		Write("\n1. SELECT e.Id, listOfInt");
		await db.Entities.Select((e) => new { e.Id, listOfInt }).ToListAsync();

		Write("\n2. SELECT e.Id, setOfInt");
		try { await db.Entities.Select((e) => new { e.Id, setOfDouble }).ToListAsync(); }
		catch (Exception e) { Console.WriteLine(e); }

		Write("\n3. SELECT e.Id, listOfInt, setOfInt");
		try { await db.Entities.Select((e) => new { e.Id, listOfInt, setOfDouble }).ToListAsync(); }
		catch (Exception e) { Console.WriteLine(e); }

		Write("\n4. SELECT e.Id, listOfInt, setOfInt, anObject");
		try { await db.Entities.Select((e) => new { e.Id, listOfInt, setOfDouble, anObject }).ToListAsync(); }
		catch (Exception e) { Console.WriteLine(e); }
	}

	public class Db : DbContext
	{
		public DbSet<Entity> Entities { get; init; } = null!;

		protected override void OnConfiguring(DbContextOptionsBuilder options)
		{
			options.UseSqlServer("...");
			options.LogTo(Console.WriteLine, LogLevel.Information);
		}
	}

	[Table("entity")]
	[PrimaryKey(nameof(Id))]
	public class Entity
	{
		[Column("id")]
		public required int Id { get; set; }
	}

	public static void Write(string s)
	{
		var c = Console.ForegroundColor;
		Console.ForegroundColor = ConsoleColor.Cyan;
		Console.WriteLine(s);
		Console.ForegroundColor = c;
	}
}

Stack traces

With setOfDouble as a HashSet<double>, the stack trace is:

An exception occurred while iterating over the results of a query for context type 'TestEfCore.Program+Db'.
System.InvalidCastException: Unable to cast object of type 'System.Collections.Generic.HashSet`1[System.Double]' to type 'System.Collections.Generic.IList`1[System.Double]'.
   at Microsoft.EntityFrameworkCore.Storage.Json.JsonCollectionOfStructsReaderWriter`2.FromJsonTyped(Utf8JsonReaderManager& manager, Object existingObject)
   at Microsoft.EntityFrameworkCore.Storage.Json.JsonValueReaderWriter`1.FromJson(Utf8JsonReaderManager& manager, Object existingObject)
   at Microsoft.EntityFrameworkCore.Storage.Json.JsonValueReaderWriter.FromJsonString(String json, Object existingObject)
   at lambda_method11(Closure, QueryContext, DbDataReader, ResultContext, SingleQueryResultCoordinator)
   at Microsoft.EntityFrameworkCore.Query.Internal.SingleQueryingEnumerable`1.AsyncEnumerator.MoveNextAsync()
   at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.ToListAsync[TSource](IQueryable`1 source, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.ToListAsync[TSource](IQueryable`1 source, CancellationToken cancellationToken)
   at TestEfCore.Program.Main() in ~\Projects\TestWeb\TestEfCore\Program.cs:line 27

As an IReadOnlySet<double> instead:

An exception occurred while iterating over the results of a query for context type 'TestEfCore.Program+Db'.
System.MissingMethodException: Cannot dynamically create an instance of type 'System.Collections.Generic.IReadOnlySet`1[System.Double]'. Reason: Cannot create an instance of an interface.
   at System.RuntimeType.ActivatorCache..ctor(RuntimeType rt)
   at System.RuntimeType.ActivatorCache.Create(RuntimeType type)
   at System.RuntimeType.IGenericCacheEntry`1.CreateAndCache(RuntimeType type)
   at System.RuntimeType.CreateInstanceOfT()
   at System.Activator.CreateInstance[T]()
   at Microsoft.EntityFrameworkCore.Storage.Json.JsonCollectionOfStructsReaderWriter`2.FromJsonTyped(Utf8JsonReaderManager& manager, Object existingObject)
   at Microsoft.EntityFrameworkCore.Storage.Json.JsonValueReaderWriter`1.FromJson(Utf8JsonReaderManager& manager, Object existingObject)
   at Microsoft.EntityFrameworkCore.Storage.Json.JsonValueReaderWriter.FromJsonString(String json, Object existingObject)
   at lambda_method11(Closure, QueryContext, DbDataReader, ResultContext, SingleQueryResultCoordinator)
   at Microsoft.EntityFrameworkCore.Query.Internal.SingleQueryingEnumerable`1.AsyncEnumerator.MoveNextAsync()
   at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.ToListAsync[TSource](IQueryable`1 source, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.ToListAsync[TSource](IQueryable`1 source, CancellationToken cancellationToken)
   at TestEfCore.Program.Main() in ~\Projects\TestWeb\TestEfCore\Program.cs:line 27

Verbose output

EF Core version

9.0.1

Database provider

Microsoft.EntityFrameworkCore.SqlServer

Target framework

.NET 9.0.102

Operating system

Windows 11

IDE

Microsoft Visual Studio Professional 2022 x64 17.12.4

[ravindUwU]

Noticed this with the SQLite provider as well, so I made a repro here: https://github.com/ravindUwU/dotnet-efcore-35568 😊

[maumar]

Problem here is that primitive collection variables are now processed as JSON parameters (https://learn.microsoft.com/en-us/ef/core/what-is-new/ef-core-9.0/whatsnew#parameterized-primitive-collections) However, our infrastructure requires JSON collections to be either arrays or implementing IList<T> (as we require them to be ordered) - in JsonCollectionOfStructsReaderWriter.FromJsonTyped we do hard cast to IList<TElement> which fails for Hashset<TElement>.

If Hashset<T> is used as a primitive collection on an entity, we throw a good exception:

 The type 'HashSet<double>' cannot be used as a primitive collection because it is not an array and does not implement 'IList<double?>'. Collections of primitive types must be arrays or ordered lists.

We should client eval primitive collections that don't implement IList