如何使用动态字符串参数执行OrderBy？

Question

我想做这个:

var orderBy = "Nome, Cognome desc";

var timb = time.Timbratures.Include("Anagrafica_Dipendente")
    .Where(p => p.CodDipendente == 1);

if(orderBy != "")
    timb = timb.OrderBy(orderBy);

是否有OrderBy可用的超载接受字符串参数？

Answer 1

如果您使用简单的LINQ到对象并且不想依赖外部库,那么实现您想要的并不困难.

该OrderBy()子句接受一个Func<TSource, TKey>从源元素获取排序键的子句.您可以在OrderBy()子句外定义函数:

Func<Item, Object> orderByFunc = null;

然后,您可以根据排序条件将其分配给不同的值:

if (sortOrder == SortOrder.SortByName)
  orderByFunc = item => item.Name;
else if (sortOrder == SortOrder.SortByRank)
  orderByFunc = item => item.Rank;

然后你可以排序:

var sortedItems = items.OrderBy(orderByFunc);

此示例假定源类型Item具有属性Name和Rank.

请注意,在此示例TKey中Object,不限制可以排序的属性类型.如果func返回一个值类型(如Int32),它将在排序时被装箱,这有点效率低下.如果您可以约束TKey到特定值类型,则可以解决此问题.

Answer 2

绝对.您可以使用Scott Guthrie博客上的LINQ Dynamic Query Library .CodePlex上还有一个更新版本.

它允许您通过传入字符串参数来创建OrderBy子句,Where子句以及其他所有内容.它非常适合创建用于排序/过滤网格等的通用代码.

var result = data
    .Where(/* ... */)
    .Select(/* ... */)
    .OrderBy("Foo asc");

var query = DbContext.Data
    .Where(/* ... */)
    .Select(/* ... */)
    .OrderBy("Foo ascending");

Answer 3

codeConcussion的另一个解决方案(/sf/answers/508577611/)

var param = "Address";    
var pi = typeof(Student).GetProperty(param);    
var orderByAddress = items.OrderBy(x => pi.GetValue(x, null));

Answer 4

您不需要外部库.以下代码适用于LINQ to SQL /实体.

    /// <summary>
    /// Sorts the elements of a sequence according to a key and the sort order.
    /// </summary>
    /// <typeparam name="TSource">The type of the elements of <paramref name="query" />.</typeparam>
    /// <param name="query">A sequence of values to order.</param>
    /// <param name="key">Name of the property of <see cref="TSource"/> by which to sort the elements.</param>
    /// <param name="ascending">True for ascending order, false for descending order.</param>
    /// <returns>An <see cref="T:System.Linq.IOrderedQueryable`1" /> whose elements are sorted according to a key and sort order.</returns>
    public static IQueryable<TSource> OrderBy<TSource>(this IQueryable<TSource> query, string key, bool ascending = true)
    {
        if (string.IsNullOrWhiteSpace(key))
        {
            return query;
        }

        var lambda = (dynamic)CreateExpression(typeof(TSource), key);

        return ascending 
            ? Queryable.OrderBy(query, lambda) 
            : Queryable.OrderByDescending(query, lambda);
    }

    private static LambdaExpression CreateExpression(Type type, string propertyName)
    {
        var param = Expression.Parameter(type, "x");

        Expression body = param;
        foreach (var member in propertyName.Split('.'))
        {
            body = Expression.PropertyOrField(body, member);
        }

        return Expression.Lambda(body, param);
    }

(CreateExpression从/sf/answers/1134603431/复制)

Answer 5

最简单和最好的解决方案:

mylist.OrderBy(s => s.GetType().GetProperty("PropertyName").GetValue(s));

Answer 6

在这里看看这个博客.它描述了一种方法,通过定义一个EntitySorter<T>.

它允许您IEntitySorter<T>传入您的服务方法并使用它如下:

public static Person[] GetAllPersons(IEntitySorter<Person> sorter)
{
    using (var db = ContextFactory.CreateContext())
    {
        IOrderedQueryable<Person> sortedList = sorter.Sort(db.Persons);

        return sortedList.ToArray();
    }
}

你可以创建一个EntitiySorter这样的:

IEntitySorter<Person> sorter = EntitySorter<Person>
    .OrderBy(p => p.Name)
    .ThenByDescending(p => p.Id);

或者像这样:

var sorter = EntitySorter<Person>
     .OrderByDescending("Address.City")
     .ThenBy("Id");

Answer 7

我是这样做的：

using System.Linq.Expressions;

namespace System.Linq
{
    public static class LinqExtensions
    {

        public static IOrderedQueryable<TSource> OrderBy<TSource>(this IQueryable<TSource> source, string field, string dir = "asc")
        {
            // parametro => expressão
            var parametro = Expression.Parameter(typeof(TSource), "r");
            var expressao = Expression.Property(parametro, field);
            var lambda = Expression.Lambda(expressao, parametro); // r => r.AlgumaCoisa
            var tipo = typeof(TSource).GetProperty(field).PropertyType;

            var nome = "OrderBy";
            if (string.Equals(dir, "desc", StringComparison.InvariantCultureIgnoreCase))
            {
                nome = "OrderByDescending";
            }
            var metodo = typeof(Queryable).GetMethods().First(m => m.Name == nome && m.GetParameters().Length == 2);
            var metodoGenerico = metodo.MakeGenericMethod(new[] { typeof(TSource), tipo });
            return metodoGenerico.Invoke(source, new object[] { source, lambda }) as IOrderedQueryable<TSource>;

        }

        public static IOrderedQueryable<TSource> ThenBy<TSource>(this IOrderedQueryable<TSource> source, string field, string dir = "asc")
        {
            var parametro = Expression.Parameter(typeof(TSource), "r");
            var expressao = Expression.Property(parametro, field);
            var lambda = Expression.Lambda<Func<TSource, string>>(expressao, parametro); // r => r.AlgumaCoisa
            var tipo = typeof(TSource).GetProperty(field).PropertyType;

            var nome = "ThenBy";
            if (string.Equals(dir, "desc", StringComparison.InvariantCultureIgnoreCase))
            {
                nome = "ThenByDescending";
            }

            var metodo = typeof(Queryable).GetMethods().First(m => m.Name == nome && m.GetParameters().Length == 2);
            var metodoGenerico = metodo.MakeGenericMethod(new[] { typeof(TSource), tipo });
            return metodoGenerico.Invoke(source, new object[] { source, lambda }) as IOrderedQueryable<TSource>;
        }

    }
}

使用 ：

example.OrderBy("Nome", "desc").ThenBy("other")

像这样工作：

example.OrderByDescending(r => r.Nome).ThenBy(r => r.other)

Answer 8

您需要使用 LINQ动态查询库才能在运行时传递参数，

这将允许像这样的 linq 语句

string orderedBy = "Description";
var query = (from p in products
            orderby(orderedBy)
            select p);