[已解决]:排序不适用于动态列

问题描述：

我有一个通用函数，例如:

I have one generic function like:

public TabMasterListViewModel GetTabMasterList(string OrderByColumn, string OrderType, int PageSize, int CurrentPage)
        {
            try
            {
                if ((CurrentPage == 0) || (PageSize == 0))
                    return null;

                IQueryable<TabMaster> query = _tabmasterRepository.GetQueryable();
                TabMasterListViewModel model = new TabMasterListViewModel();
                model.TotalItemCount = query.Count();
                if (model.TotalItemCount == 0)
                    return null;
                model.TotalPageCount = (int)Math.Ceiling((double)model.TotalItemCount / (double)PageSize);
                if (model.TotalPageCount != 1)
                {
                    if (OrderType.ToUpper() == "ASC")
                        query = query.OrderBy(x => x.colID).Skip((CurrentPage - 1) * PageSize).Take(PageSize);
                    else
                        query = query.OrderByDescending(x => x.colID).Skip((CurrentPage - 1) * PageSize).Take(PageSize);
                }
                model.ThisPageItemCount = query.Count();
                model.TabMasterList = new List<TabMasterViewModel>();
                AutoMapper.Mapper.CreateMap<TabMaster, TabMasterViewModel>()
                    .ForMember(dest => dest.colID, opt => opt.MapFrom(src => src.colID));
                model.TabMasterList = AutoMapper.Mapper.Map(query.ToList(), model.TabMasterList);

                return model;
            }
            catch (System.Exception e)
            {
                this.LogError("Error getting the TabMaster list", e);
                return null;
            }
        }

如果我使用以下行

if i am use following line

query = query.OrderBy(x => x.colID).Skip((CurrentPage - 1) * PageSize).Take(PageSize);

然后排序就可以完成.
如果我在下一行中使用OrderByColumn，则排序不起作用.

then sorting is complete working as aspect.
if i am using OrderByColumn in following line, then sorting dose not work.

if (OrderType.ToUpper() == "ASC")
                        query = query.OrderBy(x => OrderByColumn).Skip((CurrentPage - 1) * PageSize).Take(PageSize);
                    else
                        query = query.OrderByDescending(x => OrderByColumn).Skip((CurrentPage - 1) * PageSize).Take(PageSize);

请提出我想念的东西吗?

谢谢，
Imdadhusen

Please suggest what i am missing?

Thanks,
Imdadhusen

答

这是因为OrderByColumn只是一个字符串.它与您要排序的值无关:表达式x => OrderByColumn对于x的所有实例返回相同的值，因此有意义的是排序不起作用.

使它起作用是一个更有趣的问题:如果您擅长 reflection [ ^ ]，您可以跳过此答案的其余部分.如果您不喜欢反射，您仍然可以这样做:用query.OrderBy(x => ChooseColumn(x, OrderByColumn))替换您的排序表达式，并按如下方式实现ChooseColumn:

This is because OrderByColumn is just a string. It is unrelated to the values that you are sorting: expression x => OrderByColumn returns the same value for all instances of x, so it makes sense that the sort does not work.

Making it work is a more interesting question: if you are good at reflection[^], you can skip the rest of this answer. If you don''t like reflection, you can still do it: replace your sort expression with query.OrderBy(x => ChooseColumn(x, OrderByColumn)), and implement ChooseColumn as follows:

public object ChooseColumn(string columnName, TabMaster x) {
    switch(columnName) {
        case "MyColumn1": return x.MyColumn1;
        case "MyColumn2": return x.MyColumn2;
        case "MyColumn3": return x.MyColumn3;
        default: throw new InvalidOperationException("Unknown: "+columnName);
    }
}

相同的解决方案

http://landman-code.blogspot.com/2008/11/linq-to-entities-string-based-dynamic.html [

Here is the Excellent solution for the same

http://landman-code.blogspot.com/2008/11/linq-to-entities-string-based-dynamic.html[^]

[已解决]:排序不适用于动态列

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