必须在方法“Skip”异常之前调用方法“OrderBy”

我试图实施jQgrid using MvcjQgrid我得到了这个例外。

System.NotSupportedException was unhandled by user code
  Message=The method 'Skip' is only supported for sorted input in LINQ to Entities. The method 'OrderBy' must be called before the method 'Skip'.

虽然 OrdeyBy 在 Skip 方法之前使用，但为什么它会生成异常？怎么解决呢？

我在控制器中遇到了异常：

public ActionResult GridDataBasic(GridSettings gridSettings)
        {          
            var jobdescription = sm.GetJobDescription(gridSettings);
            var totalJobDescription = sm.CountJobDescription(gridSettings);

            var jsonData = new
            {
                total = totalJobDescription / gridSettings.PageSize + 1,
                page = gridSettings.PageIndex,
                records = totalJobDescription,
                rows = (
                    from j in jobdescription
                    select new
                    {
                        id = j.JobDescriptionID,
                        cell = new[] 
                    { 
                        j.JobDescriptionID.ToString(), 
                        j.JobTitle,
                        j.JobType.JobTypeName,
                        j.JobPriority.JobPriorityName,
                        j.JobType.Rate.ToString(),
                        j.CreationDate.ToShortDateString(),
                         j.JobDeadline.ToShortDateString(),

                    }
                    }).ToArray()
            };
            return Json(jsonData, JsonRequestBehavior.AllowGet);
        }

获取作业描述方法 and 计数作业描述方法

public int CountJobDescription(GridSettings gridSettings)
        {
            var jobdescription = _dataContext.JobDescriptions.AsQueryable();

            if (gridSettings.IsSearch)
            {
                jobdescription = gridSettings.Where.rules.Aggregate(jobdescription, FilterJobDescription);
            }
            return jobdescription.Count();
        }

        public IQueryable<JobDescription> GetJobDescription(GridSettings gridSettings)
        {
            var jobdescription = orderJobDescription(_dataContext.JobDescriptions.AsQueryable(), gridSettings.SortColumn, gridSettings.SortOrder);

            if (gridSettings.IsSearch)
            {
                jobdescription = gridSettings.Where.rules.Aggregate(jobdescription, FilterJobDescription);
            }

            return jobdescription.Skip((gridSettings.PageIndex - 1) * gridSettings.PageSize).Take(gridSettings.PageSize);
        }

最后FilterJobDescription 和 OrderJobDescription

private static IQueryable<JobDescription> FilterJobDescription(IQueryable<JobDescription> jobdescriptions, Rule rule)
        {
            if (rule.field == "JobDescriptionID")
            {
                int result;
                if (!int.TryParse(rule.data, out result))
                    return jobdescriptions;
                return jobdescriptions.Where(j => j.JobDescriptionID == Convert.ToInt32(rule.data));

            }

// Similar Statements

            return jobdescriptions;
        }



private IQueryable<JobDescription> orderJobDescription(IQueryable<JobDescription> jobdescriptions, string sortColumn, string sortOrder)
        {
            if (sortColumn == "JobDescriptionID")
                return (sortOrder == "desc") ? jobdescriptions.OrderByDescending(j => j.JobDescriptionID) : jobdescriptions.OrderBy(j => j.JobDescriptionID);

            return jobdescriptions;
        }

该例外意味着您always如果您申请，需要排序输入Skip，也是在用户没有单击要排序的列的情况下。我可以想象，当您第一次打开网格视图时，在用户甚至可以单击列标题之前，没有指定排序列。为了捕捉这种情况，我建议在没有给出其他排序标准时定义一些您想要的默认排序，例如：

switch (sortColumn)
{
    case "JobDescriptionID":
        return (sortOrder == "desc")
            ? jobdescriptions.OrderByDescending(j => j.JobDescriptionID)
            : jobdescriptions.OrderBy(j => j.JobDescriptionID);

    case "JobDescriptionTitle":
        return (sortOrder == "desc")
            ? jobdescriptions.OrderByDescending(j => j.JobDescriptionTitle)
            : jobdescriptions.OrderBy(j => j.JobDescriptionTitle);

    // etc.

    default:
        return jobdescriptions.OrderBy(j => j.JobDescriptionID);
}

Edit

根据您的评论，关于您的后续问题：您无法使用ToString()在 LINQ to Entities 查询中。下一个问题是你无法创建一个string查询中的数组。我建议使用其本机类型从数据库加载数据，然后将其转换为内存中的字符串（以及字符串数组）：

rows = (from j in jobdescription
        select new
        {
            JobDescriptionID = j.JobDescriptionID,
            JobTitle = j.JobTitle,
            JobTypeName = j.JobType.JobTypeName,
            JobPriorityName = j.JobPriority.JobPriorityName,
            Rate = j.JobType.Rate,
            CreationDate = j.CreationDate,
            JobDeadline = j.JobDeadline
        })
        .AsEnumerable() // DB query runs here, the rest is in memory
        .Select(a => new
        {
            id = a.JobDescriptionID,
            cell = new[] 
            { 
                a.JobDescriptionID.ToString(), 
                a.JobTitle,
                a.JobTypeName,
                a.JobPriorityName,
                a.Rate.ToString(),
                a.CreationDate.ToShortDateString(),
                a.JobDeadline.ToShortDateString()
            }
        })
        .ToArray()