如何将参数传递给Linq Orderby [重复]

Question

我需要将参数传递给 linq 查询。我的查询如下：

var appointments = (from a in inMemContext.Appointments
                    join u in inMemContext.Users on a.UserId equals u.UserId into AppointmentAssignments
                    from aa in AppointmentAssignments.DefaultIfEmpty()
                    join l in inMemContext.Languages on a.PreferredLanguage equals l.LanguageKey
                    where a.BranchId == branchId
                    && a.AppointmentDate.Date == TimeZoneInfo.ConvertTimeFromUtc(DateTime.UtcNow, TimeZoneInfo.FindSystemTimeZoneById(b.TimeZoneId)).Date 
                    orderby a.AppointmentTime
                    select new AppointmentEntryDetailsDto
                    {
                        Id = a.AppointmentId.ToString(),
                        StartTime = (a.AppointmentTime).ToString("hh:mm tt", CultureInfo.InvariantCulture),
                        AppointmentType = a.AppointmentType.AppointmentTypeName,
                    });

在上述查询中，我正在获取由AppointmentTime 排序的数据。现在我需要将动态排序值设置为升序或降序。

对于这一行：

orderby a.AppointmentTime [OrderParameter]

升序或降序。我该怎么做？

Answer 1

没有这样的内置方式。

您可以创建自定义扩展方法（因此不使用语言集成查询），或分支整个语句，或按负时间排序（在排序前根据参数转换时间，从 24:00:00 或类似）。

Answer 2

这可以通过创建一个扩展方法来实现，该方法可以动态改变它是升序还是降序：

public static class LinqExtensions
{
    public static IEnumerable<TModel> OrderByDynamic<TModel, TKey>(this IEnumerable<TModel> source, Func<TModel, TKey> selector, bool ascending = true)
    {
        if (ascending) return source.OrderBy(selector);
        return source.OrderByDescending(selector);
    }
}

用法：

var appointmentList = new List<Appointment>
{
    new Appointment { UserId = "1", PreferredLanguage = "English", BranchId = "1", AppointmentDateTime = new DateTime(2000, 1, 1, 0, 0, 0) },
    new Appointment { UserId = "2", PreferredLanguage = "Japanese", BranchId = "1", AppointmentDateTime = new DateTime(2000, 2, 1, 0, 0, 0) },
    new Appointment { UserId = "3", PreferredLanguage = "Spanish", BranchId = "2", AppointmentDateTime = new DateTime(2000, 3, 1, 0, 0, 0) },
};

// Order By Descending
var appointments = appointmentList.OrderByDynamic(selector: x => x.AppointmentDateTime, ascending: false);

这与 Linq 查询不直接兼容，但可用于任何 IEnumerable 的结果。至于如何将其用于您的具体情况，我将由您自行决定。