ASP.NET Core 6.0 MVC - Sort a string with range of date

Question

I think I am coming closer to what I want but think I could use some help.

What I found out was if I do order.by(x => x.Datum) the date gets sorted despite being a string by the format yyyy/MM/dd so far so good, now I decided to extend the string to a daterange, like so: dd/MM/yyyy-dd/mm/yyyy .

From my point of understanding, I can also convert the string to a datetime object with DateTime.ParseExact but get the following error:

FormatException: DateTime pattern 'd' appears more than once with different values

Is it not possible to store a date range in a datetime object?

public IActionResult Termin() //Diese Methode zeigt die Termine an.
{
    var termin = _context.Termin
                         .Select(x => new ViewModelExposeTermin
                                          {
                                              Id = x.Id,    
                                              Name = x.Name,    
                                              Ort  = x.Ort,
                                              Datum = x.Datum,
                                              Uhrzeit = x.Uhrzeit
                                          })
                         .ToList()
                         .OrderBy(x => DateTime.ParseExact(x.Datum, "dd/MM/yyyy-dd/MM/yyyy", CultureInfo.CurrentCulture));

    return View(termin);
}

Answer 1

I'm not sure that sql has a data-range like type, instead you could use 2 datetime fields.

public class TerminDatabaseModel
{
    /*
     * Some other properties
     */
    
    public DateTime Start { get; set; }
    public DateTime End { get; set; }
}

Then you can create your own custom DateTimeRange value type, it should implements IComparer<DateTimeRange> in order to be used in OrderBy by Linq.

public readonly struct DateTimeRange : IComparer<DateTimeRange>
{
    public DateTimeRange(DateTime start, DateTime end)
    {
        Start = start;
        End = end;
    }

    public DateTime Start { get; }
    public DateTime End { get; }
    public TimeSpan Duration => Start - End;
    
    // comparing implementation
    public int Compare(DateTimeRange x, DateTimeRange y)
    {
        return x.Duration.CompareTo(y.Duration);
    }

    /*
     * Other stuff
     */
}

and add it to your ViewModel

public class ViewModelExposeTermin
{
    /*
     * Some other properties
     */
    
    public DateTimeRange Datum { get; init; }
}

Finally, map the DateTime fields to the DateTimeRange field with

var termin = _context.Termin
        .Select(x => new ViewModelExposeTermin
        {
            Id = x.Id,    
            Name = x.Name,    
            Ort  = x.Ort,
            Datum = new DateTimeRange(x.StartDateTime, x.EndDateTime),
            Uhrzeit = x.Uhrzeit
        })
        .ToList()
        .OrderBy(x => x.Datum);

    return View(termin);

Note

The order take place after the data are retrieved from the database. To perform the sort inside the query, you have to use EF's OrderBy before fetching with ToList