该方法“排序依据”必须调用该方法“跳过”前异常(The method 'OrderBy

我试图实现jQgrid使用MvcjQgrid和我得到这个例外。

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就是为什么它是产生异常跳过方法之前使用？ 怎样才可以解决？

我遇到了在控制器中的异常：

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);
        }

GetJobDescription方法和CountJobDescription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;
        }

Answer 1:

唯一的例外意味着你总是需要一个排序的输入，如果你申请Skip ，也是在用户没有在列中单击作为排序依据的情况。 我能想象，当你打开用户之前在第一时间甚至可以单击列标题网格视图没有排序列指定。 为了赶上这种情况下，我会建议定义一些默认的排序，你希望在没有给出其他排序标准，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);
}

编辑

关于根据您的评论你的后续问题：你不能使用ToString()在LINQ到实体查询。 而接下来的问题是，你不能创建一个string在查询阵列。 我建议他们的本地类型加载从数据库中的数据，然后再把转换为字符串（和字符串数组）内存：

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()

Answer 2:

我有同样类型的问题使用从亚当·安德森一些代码，接受排序依据通用串排序排序后。

得到这个错误时抛出后，我做了很多的研究，发现非常巧妙的解决办法：

var query = SelectOrders(companyNo, sortExpression);

return Queryable.Skip(query, iStartRow).Take(iPageSize).ToList();

希望帮助！

SP

文章来源: The method 'OrderBy' must be called before the method 'Skip' Exception