Order by using Iqueryable for datatable

Question

I have following function that prepare data for jquery datatable grid. Now I am facing following error for Datatype other than string

Unable to cast the type 'System.DateTime' to type 'System.Object'. LINQ to Entities only supports casting EDM primitive or enumeration types.

Code:

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);
            }

earlier I was using IEnumerable which was first loading all data in list & then performing filter which was working fine (but not correct or best practice)

Now I am stuck with the filter part. How can I fix this error to have order by all type of property column?

I did lots of research but could not found the any solution.

Answer 1

dynamic or object cannot be used as TKey generic argument of EF Queryable.OrderBy (actually in any Queryable method expression) - it has to be the actual type of the key. Which in turn means you cannot use a common Expression<Func<...>> variable to hold the keySelector expression.

The solution is to use conditional .OrderBy[Descending] inside your switch / case block.

To make handling the ascending/descending option easier (and avoid expression duplication), start by creating a simple custom extension method like this:

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);
        }
    }
}

Then move the switch / case block after the

recordFilterd = data.Count();

line and use the above helper method inside:

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;
}