按enum描述排序

public partial class Item
{
    public enum MyEnumE
    {
        [Description("description of enum1")]
        Enum1,
        [Description("description of enum2")]
        Enum2,
        ...
    }
    public MyEnumE MyEnum { get; set; }
}

public async Task<IPagedList<Item>> Search(ItemCriteria criteria, SortableTypeE sortName, SortOrder.TypeE sortOrder, int pageNb)
    {
        var itemFilter = GenerateFilter(criteria);
        var items = entities.Items.Where(itemFilter);
        return await SortAndPaginate(items, sortName, sortOrder, pageNb);
    }
    private async Task<IPagedList<Item>> SortAndPaginate(IQueryable<Item> items, SortableTypeE sortName, SortOrder.TypeE sortOrder, int pageNb)
    {
        IOrderedQueryable<Item> result = null;
        switch (sortName)
        {
            ...
            case SortableTypeE.Type:
                result = sortOrder == SortOrder.TypeE.ASC
                    ? items.OrderBy(i => i.MyEnum.GetDescription())
                    : items.OrderByDescending(i => i.MyEnum.GetDescription());
                result = result.ThenBy(i => i.SomeOtherProperty);
                break;
            ...
        }
        if (result != null)
        {
            return await result.ToPagedListAsync(pageNb, 10);
        }
        return PagedListHelper.Empty<Item>();
    }

public static string GetDescription(this Enum e)
{
    FieldInfo fi = e.GetType().GetField(e.ToString());
    DescriptionAttribute[] attributes = (DescriptionAttribute[])fi.GetCustomAttributes(typeof(DescriptionAttribute), false);
    if (attributes.Length > 0)
        return attributes[0].Description;
    else
        return e.ToString();
}

我会选择动态表达式。它更灵活，可以很容易地进行更改，而不会影响数据库表和查询。

但是，不是通过数据库中的描述字符串排序，而是在内存中创建有序映射，将int"顺序"值与每个enum值相关联，如下所示:

public static class EnumHelper
{
    public static Expression<Func<TSource, int>> DescriptionOrder<TSource, TEnum>(this Expression<Func<TSource, TEnum>> source)
        where TEnum : struct
    {
        var enumType = typeof(TEnum);
        if (!enumType.IsEnum) throw new InvalidOperationException();
        var body = ((TEnum[])Enum.GetValues(enumType))
            .OrderBy(value => value.GetDescription())
            .Select((value, ordinal) => new { value, ordinal })
            .Reverse()
            .Aggregate((Expression)null, (next, item) => next == null ? (Expression)
                Expression.Constant(item.ordinal) :
                Expression.Condition(
                    Expression.Equal(source.Body, Expression.Constant(item.value)),
                    Expression.Constant(item.ordinal),
                    next));
        return Expression.Lambda<Func<TSource, int>>(body, source.Parameters[0]);
    }
    public static string GetDescription<TEnum>(this TEnum value)
        where TEnum : struct
    {
        var enumType = typeof(TEnum);
        if (!enumType.IsEnum) throw new InvalidOperationException();
        var name = Enum.GetName(enumType, value);
        var field = typeof(TEnum).GetField(name, BindingFlags.Static | BindingFlags.Public);
        return field.GetCustomAttribute<DescriptionAttribute>()?.Description ?? name;
    }
}

用法如下:

case SortableTypeE.Type:
    var order = EnumHelper.DescriptionOrder((Item x) => x.MyEnum);
    result = sortOrder == SortOrder.TypeE.ASC
        ? items.OrderBy(order)
        : items.OrderByDescending(order);
    result = result.ThenBy(i => i.SomeOtherProperty);
    break;

生成如下表达式:

x => x.MyEnum == Enum[0] ? 0 :
     x.MyEnum == Enum[1] ? 1 :
     ...
     x.MyEnum == Enum[N-2] ? N - 2 :
     N - 1;

0, 1, . .N-2为按描述排序的值表中对应的索引。

替代1

您可以通过将enum投影为自定义值并按其排序来实现。

的例子:

items
    .Select(x=> new 
    {
        x,
        Desc = (
            x.Enum == Enum.One ? "Desc One" 
            : x.Enum == Enum.Two ? "Desc Two" 
            ... and so on)
    })
    .OrderBy(x=>x.Desc)
    .Select(x=>x.x);

实体框架将生成如下的SQL

SELECT
    *
FROM
    YourTable
ORDER BY
    CASE WHEN Enum = 1 THEN 'Desc One'
    WHEN Enum = 2 THEN 'Desc Two'
    ...and so on
    END

如果你有很多这样的查询，你可以创建扩展方法

public static IQueryable<Entity> OrderByDesc(this IQueryable<Entity> source)
{
    return source.Select(x=> new 
    {
        x,
        Desc = (
            x.Enum == Enum.One ? "Desc One" 
            : x.Enum == Enum.Two ? "Desc Two" 
            ... and so on)
    })
    .OrderBy(x=>x.Desc)
    .Select(x=>x.x);
}

当你需要它的时候调用它

var orderedItems = items.OrderByDesc();

---

替代2

另一个可选的解决方案是创建额外的表，将枚举值映射到枚举描述，并将表连接到该表。此解决方案性能更高，因为您可以在enum描述列上创建索引。

---

替代3

如果需要基于枚举描述属性的动态表达式，可以自己构建

助手类

public class Helper
{
    public MyEntity Entity { get; set; }
    public string Description { get; set; }
}

获取动态构建表达式

public static string GetDesc(MyEnum e)
{
    var type = typeof(MyEnum);
    var memInfo = type.GetMember(e.ToString());
    var attributes = memInfo[0].GetCustomAttributes(typeof(DescriptionAttribute),
        false);
    return ((DescriptionAttribute)attributes[0]).Description;
}
private static Expression<Func<MyEntity, Helper>> GetExpr()
{
    var descMap = Enum.GetValues(typeof(MyEnum))
        .Cast<MyEnum>()
        .ToDictionary(value => value, GetDesc);
    var paramExpr = Expression.Parameter(typeof(MyEntity), "x");
    var expr = (Expression) Expression.Constant(string.Empty);
    foreach (var desc in descMap)
    {
        // Change string "Enum" below with your enum property name in entity
        var prop = Expression.Property(paramExpr, typeof(MyEntity).GetProperty("Enum")); 
        expr = Expression.Condition(Expression.Equal(prop, Expression.Constant(desc.Key)),
            Expression.Constant(desc.Value), expr);
    }

    var newExpr = Expression.New(typeof(Helper));
    var bindings = new MemberBinding[]
    {
        Expression.Bind(typeof(Helper).GetProperty("Entity"), paramExpr),
        Expression.Bind(typeof(Helper).GetProperty("Description"), expr)
    };
    var body = Expression.MemberInit(newExpr, bindings);
    return (Expression<Func<MyEntity, Helper>>) Expression.Lambda(body, paramExpr);
}

这样命名

var e = GetExpr();
items.Select(e)
    .OrderBy(x => x.Description)
    .Select(x => x.Entity);

将我的数据库列改为字符串(枚举描述)枚举本身的(但对我来说听起来像一个hack)。

相反，对于数据驱动的应用程序，最好在数据库引用表 MyItemProperty(MyPropKey,MyPropDescription)中描述Item属性，并在Items表中包含MyPropKey列。

它有几个好处，例如

• 允许添加新的属性值而无需更改代码;
• 允许编写包含数据库中所有信息的SQL报告，而无需编写c#;
• 性能优化可以在SQL上完成只需请求一个页面即可完成关卡;
没有枚举，没有需要维护的代码。

为了保持简单和良好的性能，我会手动订购枚举，您只需要做一次，它将帮助很多

public enum MyEnumE
{
    Enum1 = 3,
    Enum2 = 1,
    Enum3 = 2, // set the order here... 
}

下面是一个使用join的简化示例:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Reflection;
namespace ConsoleApplication
{
    public partial class Item
    {
        public enum MyEnumE
        {
            [Description("description of enum1")]
            Enum1,
            [Description("description of enum2")]
            Enum2
        }
        public Item(MyEnumE myEnum)
        {
            MyEnum = myEnum;
        }
        public MyEnumE MyEnum { get; set; }
    }
    class Program
    {
        private static IEnumerable<KeyValuePair<int, int>> GetEnumRanks(Type enumType)
        {
            var values = Enum.GetValues(enumType);
            var results = new List<KeyValuePair<int, string>>(values.Length);
            foreach (int value in values)
            {
                FieldInfo fieldInfo = enumType.GetField(Enum.GetName(enumType, value));
                var attribute = (DescriptionAttribute)fieldInfo.GetCustomAttribute(typeof(DescriptionAttribute));
                results.Add(new KeyValuePair<int, string>(value, attribute.Description));
            }
            return results.OrderBy(x => x.Value).Select((x, i) => new KeyValuePair<int, int>(x.Key, i));
        }
        static void Main(string[] args)
        {
            var itemsList = new List<Item>();
            itemsList.Add(new Item(Item.MyEnumE.Enum1));
            itemsList.Add(new Item(Item.MyEnumE.Enum2));
            itemsList.Add(new Item(Item.MyEnumE.Enum2));
            itemsList.Add(new Item(Item.MyEnumE.Enum1));
            IQueryable<Item> items = itemsList.AsQueryable();
            var descriptions = GetEnumRanks(typeof(Item.MyEnumE));
            //foreach (var i in descriptions)
            //  Console.WriteLine(i.Value);
            var results = items.Join(descriptions, a => (int)a.MyEnum, b => b.Key, (x, y) => new { Item = x, Rank = y.Value }).OrderBy(x => x.Rank).Select(x => x.Item);
            foreach (var i in results)
                Console.WriteLine(i.MyEnum.ToString());
            Console.WriteLine("'nPress any key...");
            Console.ReadKey();
        }
    }
}

我有一个类似的问题要解决，只是我的排序必须是动态，即按列排序参数是一个string。

boolean排序也必须自定义，因为true在false之前(例如;"Active"在"Inactive"之前)。

我在这里与您分享完整的代码，以便您可以节省时间。如果你发现有改进的地方，请随时在评论中分享。

private static IQueryable<T> OrderByDynamic<T>(this IQueryable<T> query, SortField sortField)
{
    var queryParameterExpression = Expression.Parameter(typeof(T), "x");
    var orderByPropertyExpression = GetPropertyExpression(sortField.FieldName, queryParameterExpression);
    Type orderByPropertyType = orderByPropertyExpression.Type;
    LambdaExpression lambdaExpression = Expression.Lambda(orderByPropertyExpression, queryParameterExpression);
    if (orderByPropertyType.IsEnum)
    {
        orderByPropertyType = typeof(int);
        lambdaExpression = GetExpressionForEnumOrdering<T>(lambdaExpression);
    }
    else if (orderByPropertyType == typeof(bool))
    {
        orderByPropertyType = typeof(string);
        lambdaExpression =
            GetExpressionForBoolOrdering(orderByPropertyExpression, queryParameterExpression);
    }
    var orderByExpression = Expression.Call(
        typeof(Queryable),
        sortField.SortDirection == SortDirection.Asc ? "OrderBy" : "OrderByDescending",
        new Type[] { typeof(T), orderByPropertyType },
        query.Expression,
        Expression.Quote(lambdaExpression));
    return query.Provider.CreateQuery<T>(orderByExpression);
}

共享的GetPropertyExpression已经被简化了一点，以排除嵌套的属性处理。

private static MemberExpression GetPropertyExpression(string propertyName, ParameterExpression queryParameterExpression)
{
    MemberExpression result = Expression.Property(queryParameterExpression, propertyName);
    return result;
}

下面是稍微修改过的代码(来自被接受的解决方案)来处理Enum排序。

private static Expression<Func<TSource, int>> GetExpressionForEnumOrdering<TSource>(LambdaExpression source)
{
    var enumType = source.Body.Type;
    if (!enumType.IsEnum)
        throw new InvalidOperationException();
    var body = ((int[])Enum.GetValues(enumType))
        .OrderBy(value => GetEnumDescription(value, enumType))
        .Select((value, ordinal) => new { value, ordinal })
        .Reverse()
        .Aggregate((Expression)null, (next, item) => next == null ? (Expression)
            Expression.Constant(item.ordinal) :
            Expression.Condition(
                Expression.Equal(source.Body, Expression.Convert(Expression.Constant(item.value), enumType)),
                Expression.Constant(item.ordinal),
                next));
    return Expression.Lambda<Func<TSource, int>>(body, source.Parameters[0]);
}

以及boolean排序。

private static LambdaExpression GetExpressionForBoolOrdering(MemberExpression orderByPropertyExpression, ParameterExpression queryParameterExpression)
{
    var firstWhenActiveExpression = Expression.Condition(orderByPropertyExpression,
        Expression.Constant("A"),
        Expression.Constant("Z"));
    return Expression.Lambda(firstWhenActiveExpression, new[] { queryParameterExpression });
}

GetEnumDescription也被修改为接收Type作为参数，所以它可以不需要泛型来调用。

private static string GetEnumDescription(int value, Type enumType)
{
    if (!enumType.IsEnum)
        throw new InvalidOperationException();
    var name = Enum.GetName(enumType, value);
    var field = enumType.GetField(name, BindingFlags.Static | BindingFlags.Public);
    return field.GetCustomAttribute<DescriptionAttribute>()?.Description ?? name;
}

SortField是一个简单的抽象，包含要排序的string列属性和排序的direction。为了简单起见，我在这里也不分享这个。

干杯!