asp.net-mvc-3 – 方法“OrderBy”必须在方法“跳过”异常之前调用

我试图使用MvcjQgrid实现jQgrid,我得到这个异常.

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'.

虽然OrdeyBy在Skip方法之前使用为什么会生成异常？怎么解决？

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;
        }

解决方法

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

关于您的后续问题根据您的评论：您不能在LINQ to Entities查询中使用ToString().而下一个问题是您无法在查询中创建一个字符串数组.我建议从数据库中加载其原始类型的数据,然后将其转换为内存中的字符串(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()

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