无法使用LINQ OrderBy中的属性名进行排序

Question

错误是

  

LINQ to Entities无法识别方法'System.Object   GetValue（System.Object，System.Object []）'方法和此方法   无法翻译成商店表达。

我的代码是

public static GridResult GetAllUsers(int count, int tblsize,string sortcreteria)
{
      using (UserEntities entity = new UserEntities())
      {

          var data = entity.User_Details.Take(count)
.OrderBy(i =>.GetType().GetProperty(sortcreteria).GetValue(i,null))
.Skip(tblsize).ToList();
          result.DataSource = data;
          result.Count = entity.User_Details.Count();
      }
      return result;
}

如何使用属性名称作为字符串进行排序？

Answer 1

只需将以下扩展名添加到您的代码中即可：

using System.Linq;
using System.Linq.Expressions;
using System;

namespace SomeNameSpace
{
    public static class SomeExtensionClass
    {
        public static IQueryable<T> OrderByField<T>(this IQueryable<T> q, string SortField, bool Ascending)
        {
            var param = Expression.Parameter(typeof(T), "p");
            var prop = Expression.Property(param, SortField);
            var exp = Expression.Lambda(prop, param);
            string method = Ascending ? "OrderBy" : "OrderByDescending";
            Type[] types = new Type[] { q.ElementType, exp.Body.Type };
            var mce = Expression.Call(typeof(Queryable), method, types, q.Expression, exp);
            return q.Provider.CreateQuery<T>(mce);
        }
    }

}

<强>用法：

.OrderByField(sortcriteria, true)

修改

要获得对ThenBy方法的支持，请返回IOrderedQueryable的以下方法应该完成所有工作：

public static class SomeExtensionClass
{
    private static IOrderedQueryable<T> OrderingHelper<T>(IQueryable<T> source, string propertyName, bool descending, bool anotherLevel)
    {
        var param = Expression.Parameter(typeof(T), "p");
        var property = Expression.PropertyOrField(param, propertyName);
        var sort = Expression.Lambda(property, param);

        var call = Expression.Call(
            typeof(Queryable),
            (!anotherLevel ? "OrderBy" : "ThenBy") + (descending ? "Descending" : string.Empty),
            new[] { typeof(T), property.Type },
            source.Expression,
            Expression.Quote(sort));

        return (IOrderedQueryable<T>)source.Provider.CreateQuery<T>(call);
    }

    public static IOrderedQueryable<T> OrderBy<T>(this IQueryable<T> source, string propertyName)
    {
        return OrderingHelper(source, propertyName, false, false);
    }

    public static IOrderedQueryable<T> OrderBy<T>(this IQueryable<T> source, string propertyName, bool descending)
    {
        return OrderingHelper(source, propertyName, descending, false);
    }

    public static IOrderedQueryable<T> ThenBy<T>(this IOrderedQueryable<T> source, string propertyName)
    {
        return OrderingHelper(source, propertyName, false, true);
    }

    public static IOrderedQueryable<T> ThenBy<T>(this IOrderedQueryable<T> source, string propertyName, bool descending)
    {
        return OrderingHelper(source, propertyName, descending, true);
    }
}

Answer 2

你可以尝试使用（有点旧的）Dynamic LINQ库来执行此操作：

var data = entity.User_Details
    .Take(count)
    .OrderBy(sortcriteria)
    .Skip(tblsize)
    .ToList();

或者，您仍然可以先使用原始查询对序列进行排序，因为LINQ to Entities提供程序无法将对Reflection API的调用转换为SQL：

var data = entity.User_Details
    .Take(count)
    .Skip(tblsize)
    .AsEnumerable()
    .OrderBy(i => i.GetType().GetProperty(sortcriteria).GetValue(i, null))

Answer 3

您可能需要使用Expression Trees来构建Linq语句OrderBy(x => x.SomeProperty)。

Create an OrderBy Expression for LINQ/Lambda

Create LINQ to entities OrderBy expression on the fly