如何设置IQueryable的类型为函数返回的类型？？

private IQueryable GetArticleQueryByColumnID(long columnID)
        {
            string sqlStr = "";
            if (columnID > 0)
            {
                sqlStr = string.Format(ExSql, string.Format(" and COLUMN_ID={0} ", columnID));
            }
            else
            {
                sqlStr = string.Format(ExSql, "");
            }
            switch (GetColumn(columnID).REFER_TYPE)
            {
                case 0:
                    return _db.ExecuteQuery<V_ARTICLE_SHOW_ALL>(sqlStr).AsQueryable();
                case 1:
                    return _db.ExecuteQuery<V_ARTICLE_SHOW_REFER>(sqlStr).AsQueryable();
                case 2:
                    return _db.ExecuteQuery<V_ARTICLE_SHOW_REFER>(sqlStr).AsQueryable();
                case 3:
                    return _db.ExecuteQuery<V_ARTICLE_SHOW_DUTYTREE>(sqlStr).AsQueryable();
                default:
                    return _db.ExecuteQuery<V_ARTICLE_SHOW_REFER_ALL>(sqlStr).AsQueryable();
            } 
 
        }

因为没有办法判断具体返回的集合类型
调用 GetArticleQueryByColumnID(columnID).Count();时报错：

错误7“System.Linq.IQueryable”不包含“Count”的定义，并且找不到可接受类型为“System.Linq.IQueryable”的第一个参数的扩展方法“Count”(是否缺少 using 指令或程序集引用?)D:\newcode2013\DWGK\DWGK\ZWW.BLL\Special\SpecialDAL.cs26825ZWW.BLL
asp.net??? IQueryable
[解决办法]

private IQueryable<MyClass> GetArticleQueryByColumnID(long columnID)
        {
            string sqlStr = "";
            if (columnID > 0)
            {
                sqlStr = string.Format(ExSql, string.Format(" and COLUMN_ID={0} ", columnID));
            }
            else
            {
                sqlStr = string.Format(ExSql, "");
            }
            switch (GetColumn(columnID).REFER_TYPE)
            {
                case 0:
                    return _db.ExecuteQuery<V_ARTICLE_SHOW_ALL>(sqlStr).AsQueryable().Select(x=>new MyClass{});
                case 1:
                    return _db.ExecuteQuery<V_ARTICLE_SHOW_REFER>(sqlStr).AsQueryable().Select(x=>new MyClass{}); 
 
                case 2:
                    return _db.ExecuteQuery<V_ARTICLE_SHOW_REFER>(sqlStr).AsQueryable().Select(x=>new MyClass{});
                case 3:
                    return _db.ExecuteQuery<V_ARTICLE_SHOW_DUTYTREE>(sqlStr).AsQueryable().Select(x=>new MyClass{});
                default:
                    return _db.ExecuteQuery<V_ARTICLE_SHOW_REFER_ALL>(sqlStr).AsQueryable().Select(x=>new MyClass{});
            }
        }

或者直接返回Dynamic