通过使用Iqueryable对数据表进行排序

Question

我有以下函数为jquery数据表网格准备数据.现在我面临除字符串以外的数据类型的跟随错误

无法将类型"System.DateTime"强制转换为"System.Object"类型.LINQ to Entities仅支持转换EDM原语或枚举类型.

码:

public GeneralResponse<IEnumerable<Holiday>> GetHolidays(string filter, 
                int initialPage, 
                int pageSize, 
                out int totalRecords, 
                out int recordFilterd,
                int sortColumn, 
                string sortDirection)
            {
                var response = new GeneralResponse<IEnumerable<Holiday>>();
                totalRecords = 0;
                recordFilterd = 0;
                filter = filter.Trim().ToLower();
                try
                {
                    Expression<Func<Holiday, dynamic>> expr;
                    switch (sortColumn)
                    {
                        case 0:
                            expr = p => p.HolidayDate;
                            break;
                        case 1:
                            expr = p => p.Name;
                            break;
                        case 2:
                            expr = p => p.ExchangeMarket.Name;
                            break;
                        default:
                            expr = p => p.CreatedOn;
                            break;
                    }
                    var data = holidayRepository.Query(true);
                  //var data = holidayRepository.GetAll(true).AsQueryable(); previous working one



                    totalRecords = data.Count();
                    //filter 
                    if (!string.IsNullOrWhiteSpace(filter))
                    {
                        data = data.Where(x => x.Name.ToLower().Contains(filter));
                        //todo : Add date search as well 
                    }
                    recordFilterd = data.Count();
                    //sort 
                    data = sortDirection == "asc" ? data.OrderBy(expr) : data.OrderByDescending(expr);

                    data = data
                        .Skip(initialPage * pageSize)
                        .Take(pageSize);

                    var result = data.ToList();
                    response.Data = result;

                }
                catch (Exception e)
                {
                    response.Error = true;
                    response.Exception = e;
                }
                return response;
            }

// This method is under generic repository 
     public IQueryable<T> Query()
            {
               return Query(false);
            }

早些时候我正在使用IEnumerable,它首先加载列表中的所有数据然后执行过滤器工作正常(但不正确或最佳实践)

现在我被困在过滤器部分.如何通过所有类型的属性列修复此错误以获得订单？

我做了很多研究,但找不到任何解决方案.

Answer 1

dynamic或者object不能用作TKeyEF的通用参数Queryable.OrderBy(实际上在任何Queryable方法表达式中) - 它必须是键的实际类型.这反过来意味着您不能使用公共Expression<Func<...>>变量来保存keySelector表达式.

解决方案是.OrderBy[Descending]在switch/ caseblock中使用条件.

要更容易处理升序/降序选项(并避免表达式重复),首先要创建一个简单的自定义扩展方法,如下所示:

namespace System.Linq
{
    public static class QueryableExtensions
    {
        public static IOrderedQueryable<TSource> OrderBy<TSource, TKey>(this IQueryable<TSource> source, Expression<Func<TSource, TKey>> keySelector, bool ascending)
        {
            return ascending ? source.OrderBy(keySelector) : source.OrderByDescending(keySelector);
        }
    }
}

然后移动switch/ case块后

recordFilterd = data.Count();

行并使用上面的helper方法:

bool ascending = sortDirection == "asc";
switch (sortColumn)
{
    case 0:
        data = data.OrderBy(p => p.HolidayDate, ascending);
        break;
    case 1:
        data = data.OrderBy(p => p.Name, ascending);
        break;
    case 2:
        data = data.OrderBy(p => p.ExchangeMarket.Name, ascending);
        break;
    default:
        data = data.OrderBy(p => p.CreatedOn, ascending);
        break;
}