.NET 6与EF Core 6按星期分组统计问题求助

我有一张发票表，希望按星期几对运营数据进行周度分析。以下SQL查询可正常执行：

select DATENAME(weekday, [InvoiceDate]) as Day, sum([TotalPrice]) as PurchaseAmount, count(*) as VisitCount
from [Invoices]
group by DATENAME(weekday, [InvoiceDate]);

预期结果为按星期名称（如星期一、星期二等）分组，每条数据对应该星期的采购总金额（PurchaseAmount）和访问次数（VisitCount）。

但我编写的以下.NET 6和EF Core代码无法正常运行，返回null或抛出异常，恳请指导：

var results = _db.Invoices.GroupBy(i => new { i.InvoiceDate.DayOfWeek}).Select(x =>
            new DailyStatistics
            {
                Day = x.Key.ToString(),
                PurchaseAmount = x.Sum(s => s.TotalPrice),
                VisitCount = x.Count()
            }).ToList();

内容的提问来源于stack exchange，提问作者Amir Hussein Khaniki