“ System.Linq.IQueryable”不包含“ GroupBy”的定义

Question

I am having a strange issue, i am writing out a small method to use the System.Linq.Dynamic classes to query a list of objects though i do not think my issue lies with the Dynamic namespace. For some reason GroupBy and OrderByDescending cannot bed found. I already have a reference to System.Linq which is what i initially thought would have caused this... Weirdly it is finding OrderBy and other Linq methods.. My Code is below.

using System;
using System.Collections.Generic;
using System.Linq.Dynamic;
using System.Linq;
using System.Web;

namespace MvcTemplate.jrSite.Core
{
    public static class DynamicQuery
    {
        public static IQueryable Query(IQueryable items, string where, string select, string groupby, string orderby, string orderbydesc, int take)
        {
            var ret = items;

            if (where != null && where.Length != 0)
            {
                ret = ret.Where(where);
            }

            if (select != null && select.Length != 0)
            {
                ret = ret.Select(select);
            }

            if (groupby != null && groupby.Length != 0)
            {
                ret = ret.GroupBy(groupby);
            }

            if (orderby != null && orderby.Length != 0)
            {
                ret = ret.OrderBy(orderby);
            }

            if (orderbydesc != null && orderbydesc.Length != 0)
            {
                ret = ret.OrderByDescending(orderbydesc);
            }

            return ret;
        }
    }
}

Answer 1

I assume that you are using System.Linq.Dynamic project. Your methods are not found because they do not exist.

1) GroupBy form System.Linq.Dynamic:

public static IQueryable GroupBy(this IQueryable source, 
    string keySelector, string elementSelector, params object[] values) {

this method requires three parameters and your code provides two - you have to provide elementSelector .

2) The method OrderByDescending is not even declared in the source of that library. And System.Linq will not help you either as you are using non generic IQueryable . All extension methods are provided only for strongly typed queries.