CreateAggregate state is shared, breaking multiple use of an aggregate function in the same query

using SqliteConnection connection = new SqliteConnection(new SqliteConnectionStringBuilder
{
    DataSource = "A",
    Mode = SqliteOpenMode.Memory
}.ToString());
connection.Open();

using (var command = connection.CreateCommand())
{
    command.CommandText = "CREATE TABLE [test](a, b, c);";
    command.ExecuteNonQuery();

    command.CommandText = "INSERT INTO [test](a, b, c) VALUES(1, 2, 3)";
    command.ExecuteNonQuery();
    command.ExecuteNonQuery();
}
connection.CreateAggregate(
    "testCount",
    new AggClass(),
    (AggClass agg, int number) =>
    {
        agg.Counter++;
        return agg;
    },
    agg => agg.Counter);
using (var command = connection.CreateCommand())
{
    command.CommandText = "SELECT testCount(a), testCount(b), count(a), count(b) FROM [test];";
    using var reader = command.ExecuteReader();
    reader.Read();
    Console.WriteLine((reader.GetInt32(0), reader.GetInt32(1), reader.GetInt32(2), reader.GetInt32(3))); // (4, 4, 2, 2)
}

Microsoft.Data.Sqlite version: 5.0.10 Target framework: (e.g. .NET 5.0) .NET 5.0 Operating system: Windows 10 / MacOS 11.5.2

[wzchua]

It doesn’t work with struct.

as a workaround I’m using something like this

var handle = connection.Handle;
var map = new Dictionary<sqlite3_context, AggClass>();
raw.sqlite3_create_function(handle, "testCount2", 1, map,
    static (ctx, data, values) =>
    {
        var map = (Dictionary<sqlite3_context, AggClass>)data;
        if (!map.TryGetValue(ctx, out AggClass? i))
        {
            i = new AggClass();
            map.Add(ctx, i);
        }

        i.Counter++;
    },
     static(ctx, data) =>
    {
        var map = (Dictionary<sqlite3_context, AggClass>)data;
        if (!map.Remove(ctx, out AggClass? i))
        {
            raw.sqlite3_result_int(ctx, 0);
            return;
        }
        
        raw.sqlite3_result_int(ctx, i.Counter);
    });

[bricelam]

@pimbrouwers https://github.com/dotnet/efcore/issues/26070#issuecomment-926817699 gives a sketch of the solution if you’re interested in giving it a go.