11

我试图实现jQgrid使用MvcjQgrid，我得到了这个异常。

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'.

尽管在 Skip 方法之前使用了 OrdeyBy，但为什么它会生成异常？如何解决？

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);
        }

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);
        }

最后是 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;
        }
4

2 回答 2

16

例外情况意味着，如果您应用，您总是需要一个排序的输入，即使Skip在用户没有单击要排序的列的情况下也是如此。我可以想象，当您第一次打开网格视图时，用户甚至可以单击列标题之前没有指定排序列。为了抓住这种情况，我建议在没有给出其他排序标准时定义一些你想要的默认排序，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);
}

编辑

根据您的评论，关于您的后续问题：您不能ToString()在 LINQ to Entities 查询中使用。下一个问题是您不能string在查询中创建数组。我建议使用它们的本机类型从数据库加载数据，然后在内存中转换为字符串（和字符串数组）：

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()
于 2012-07-21T16:06:53.303 回答
4

在使用Adam Anderson的一些代码进行排序后，我遇到了相同类型的问题，该代码接受了 OrderBy 中的通用排序字符串。

得到这个例外后，我做了很多研究，发现非常聪明的解决方法：

var query = SelectOrders(companyNo, sortExpression);

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

希望有帮助！

SP

于 2013-11-21T01:57:01.150 回答