LINQ如何动态使用多个ThenBy？

Question

我不认为这会如此罕见，但看起来确实如此。情况是这样的。

我有一个 ApplySort 方法，它接受从 mvc 页面发布的 3 个参数。

    private List<dynamic> ApplySort(List<dynamic> listToBeSorted, string sortBy, string sortOrder)
    {
        if (String.IsNullOrEmpty(sortBy))
            sortBy = "createddate";
        if (String.IsNullOrEmpty(sortOrder) || sortOrder.Trim() != "0")
            sortOrder = "1"; // 1 = descending, 0 = ascending
        if (sortOrder == "1")
        {
            switch (sortBy)
            {
                case "name":
                    listToBeSorted = listToBeSorted.OrderByDescending(a => a.name).ToList();
                    break;
                case "assigned":
                    listToBeSorted = listToBeSorted.OrderByDescending(a => a.title).ToList();
                    break;
                case "duedate":
                    listToBeSorted = listToBeSorted.OrderByDescending(a => a.end).ToList();
                    break;
                case "status":
                    listToBeSorted = listToBeSorted.OrderByDescending(a => a.title).ToList();
                    break;
                default:
                    listToBeSorted = listToBeSorted.OrderByDescending(a => a.title).ToList();
                    break;
            }
        }
        else
        {
            // same code as in if-block, with just OrderBy calls instead of OrderByDescending
        }
        return listToBeSorted;
    }

两个问题：

1) 方法似乎过长（if 和 else 块中的代码非常相似）。

2) 我希望能够使用多个列进行排序。 sortBy 参数可以具有诸如“名称、标题、创建日期、状态”之类的值。所以应用的排序应该是，首先按名称，然后按标题，然后按创建日期......等等。 我可以通过顺序检查参数来使用 ThenBy。 但是如何根据参数值动态应用 ThenBy 链，其中 ThenBy 的数量可以变化。

string[] sortParams = sortBy.Split(new string[] { "," }, StringSplitOptions.RemoveEmptyEntries);
listToBeSorted.OrderBy(i=>i.sortParams[0]).ThenBy(j=>j.sortParams[1]).ThenBy(k=>k.sortParams[2])...(so on till sortParams.length)

我该怎么做？另外，如何使用 sortOrder 参数在同一行中按升序或降序进行排序，而不是使用 if-else。

Answer 1

您可以创建字典，将Func<string, IComparable> 映射到您的类的属性。

public class ItemWithProperty
{
    public string Property { get; set; }
}

public static void Main()
{
    Dictionary<string, Func<ItemWithProperty, IComparable>> stringPropertyMap = new Dictionary<string, Func<ItemWithProperty, IComparable>>()
    {
       {"param1", item => item.Property}
    };

    List<ItemWithProperty> toBeOrdered = new List<ItemWithProperty>();

    string[] parameters = {"param1"};
    var sorted = toBeOrdered.OrderBy(stringPropertyMap[parameters[0]]);
}

Answer 2

如果你改变你的方法签名，你会使用这个：

    private static IEnumerable<dynamic> ApplySort(IEnumerable<dynamic> listToBeSorted, ICollection<KeyValuePair<string, string>> sorters)
    {
        var orderBy = (sorters == null || sorters.Count == 0) ? new KeyValuePair<string, string>("createddate", "1") : sorters.First();
        var thenBys = (sorters == null || sorters.Count == 1) ? new List<KeyValuePair<string, string>>() : sorters.Except(Enumerable.Repeat(orderBy, 1));

        var orderedEnumerable = orderBy.Value == "1"
            ? listToBeSorted.OrderBy(x => GetPropertyValue(x, orderBy.Key))
            : listToBeSorted.OrderByDescending(x => GetPropertyValue(x, orderBy.Key));

        orderedEnumerable = thenBys.Aggregate(orderedEnumerable, (current, thenBy) => thenBy.Value == "1"
            ? current.ThenBy(x => GetPropertyValue(x, thenBy.Key))
            : current.ThenByDescending(x => GetPropertyValue(x, thenBy.Key)));

        return orderedEnumerable.ToList();
    }

    private static object GetPropertyValue(dynamic obj, string propName)
    {
        Type t = obj.GetType();
        return t.GetProperty(propName).GetValue(obj, null);
    }

试试：

    static void Main(string[] args)
    {
        var list = new List<dynamic>();
        list.Add(new { name = "Billy" });
        list.Add(new { name = "Johnny" });
        list.Add(new { name = "Ali" });

        var list2 = ApplySort(list, new List<KeyValuePair<string, string>>(new List<KeyValuePair<string, string>> { new KeyValuePair<string, string>("name", "1") }));

        foreach (var o in list2)
        {
            Console.WriteLine(o.name);
        }

        Console.ReadLine();

    }