实体LINQ不能识别查询中的方法

我有以下代码，给了我一个错误，说LINQ到实体不识别方法GetShippingHour:

private IEnumerable<OrderDTO> GetAllFixedOrders(DateTime date)
    {
        var clientSet = _context.Set<Client>();
        var orderSubstitutes = _context.Set<OrderSubstitution>()
                                .Include(o=>o.Order.Client)
                                .ForCurrentDay(date)
                                .Select(os => new { os.OrderId, os.FixedOrderId });
        var orderList = _context.Set<FixedOrder>()
            .Include(fo => fo.Client)
           .ForCurrentDay(date)
           .Where(fo => !fo.Client.IsInactive)
           .ConsideringOrderSubstitution(orderSubstitutes.Select(os => os.FixedOrderId).ToList())
           .Join(clientSet
               , o => o.ClientId
               , c => c.Id
               , (o, c) =>
                   new OrderDTO
                   {
                       OrderId = orderSubstitutes.Where(os => os.FixedOrderId == o.Id).Select(os => os.OrderId).FirstOrDefault() ?? 0,
                       ClientId = c.Id,
                       ClientName = c.Name,
                       HasFixedOrders = true,
                       FixedOrderId   = o.Id,
                       ShippingHour = GetShippingHour(c,date),
                       HasSpecialProducts = false
                   }
           ).ToList();
        return orderList;
    }
    private string GetShippingHour(Client c, DateTime date)
    {
        var dayOfWeek = date.DayOfWeek.ToString();
        string result;
        switch (dayOfWeek)
        {
            case "Sunday":
                result = c.ShippingHourSunday ?? c.ShippingHour;
                break;
            case "Monday":
                result = c.ShippingHourMonday ?? c.ShippingHour;
                break;
            case "Tuesday":
                result = c.ShippingHourTuesday ?? c.ShippingHour;
                break;
            case "Wednesday":
                result = c.ShippingHourWednesday ?? c.ShippingHour;
                break;
            case "Thursday":
                result = c.ShippingHourThursday ?? c.ShippingHour;
                break;
            case "Friday":
                result = c.ShippingHourFriday ?? c.ShippingHour;
                break;
            case "Saturday":
                result = c.ShippingHourSaturday ?? c.ShippingHour;
                break;
            default:
                result = c.ShippingHour;
                break;
        }
        return result;
    }

问题是，根据星期几的不同，我需要从Clients表的不同字段获取ShippingHour的值。问题是LINQ到实体正试图翻译我的方法。我不知道如何重写这个查询做所需的结果。