如何在Dynamic Linq中使用Enums?
我想在动态LINQ查询中使用枚举。
是否可能,如果,如何?
考虑下面的代码:
using System; using System.Collections.Generic; using System.Linq; using System.Linq.Dynamic; namespace ConsoleApplication2 { class Program { static void Main(string[] args) { Room aRoom = new Room() { Name = "a Room" }; Room bRoom = new Room() { Name = "b Room" }; Room cRoom = new Room() { Name = "c Room" }; House myHouse = new House { Rooms = new List(new Room[] { aRoom }), MainRoom = aRoom }; House yourHouse = new House() { Rooms = new List(new Room[] { bRoom, cRoom }), MainRoom = bRoom }; House donaldsHouse = new House() { Rooms = new List(new Room[] { aRoom, bRoom, cRoom }), MainRoom = aRoom }; var houses = new List(new House[] { myHouse, yourHouse, donaldsHouse }); // MainRoom.Name = \"a Room\" and Rooms.Count = 3 or // ????????????????????????? var aRoomsHouses = houses.AsQueryable().Where("MainRoom.Type = \"RoomType.Kitchen\""); Console.WriteLine("aRoomsHouses count = {0}", aRoomsHouses.Count()); Console.ReadKey(); } } public class House { public string Address { get; set; } public double Area { get; set; } public Room MainRoom { get; set; } public List Rooms { get; set; } } public class Room { public double Area { get; set; } public string Name { get; set; } public RoomType Type { get; set; } } public enum RoomType { Kitchen, Bedroom, Library, Office } }
这有效:
houses.AsQueryable() .Where("MainRoom.Type = ConsoleApplication2.RoomType.Kitchen")
我遇到了同样的问题并尝试了@Steve Wilkes指定的标记答案,但它对我不起作用!! 然后我发现动态LINQ在同一个包中有一个HTML文档,它提到可以将Enums指定为String Literals。
houses.AsQueryable().Where("MainRoom.Type = \"Kitchen\"")
这对我有用。
这应该工作
houses.AsQueryable().Where(rs=>rs.MainRoom.Type == RoomType.Kitchen);
在这种情况下,为什么需要动态linq? 你期望什么输出
根据我的喜好,应避免使用容易出错的字符串。 如果您的类或属性名称发生更改,则在遇到错误之前,您将无法找到错误。
而是使用表达
Expression> filter = (p) => p.MainRoom.Type == RoomType.Kitchen; filter = (p) => p.MainRoom.Area > 200; filter = (p) => p.Rooms.Sum(rs => rs.Area) > 500; filter = (p) => p.Address.Contains("abc"); filter = (p) => p.Area > 200; ... var aRoomsHouses = houses.AsQueryable().Where(filter);
您可以在决定使用哪个字符串filter的位置创建表达式。 更好地创建一个静态类,或者可以是switch语句,它为您提供了不同类型的表达式,您可以将其用作where参数。
另外还有一个变体使用参数
var aRoomsHouses = houses.AsQueryable().Where("MainRoom.Type = @0",RoomType.Kitchen);
要向动态linq添加新的枚举类型,必须添加以下代码:
typeof(Enum), typeof(T) T : Enum type
在预定义的动态类型中,这对我有用;