what types should be in a view model?

Joel, Rafael, Byron and I just had a conversation about flattening domain objects to view models with AutoMapper. Rafael suggested that almost everything should end up as a string on the display model as that is what any one data point displayed in HTML is going to end up as anyway. This means that when one flattens a DateTime to a string, that there is a need to make the DateTime presentable as it is being flattened. For example, the absence of .AddFormatter<TextBoxDateFormatter>() below would make the string version of the DateTime by way of a .ToString() operation, creating a very ugly string for a user to see.

private static void CreateGlobalFormatters()

{

   Mapper.ForSourceType<DateTime>().AddFormatter<TextBoxDateFormatter>();

}

 
 

TextBoxDateFormatter:

using System;

using OurApp.Core.Infrastructure;

using AutoMapper;

namespace OurApp.Web.UI.Config.AutoMapper.Formatters

{

   public class TextBoxDateFormatter : IValueFormatter

   {

      public string FormatValue(ResolutionContext context)

      {

         DateTime? value = context.SourceValue as DateTime?;

         return value.HasValue ? value.Value.ToString(DefaultFormats.TextBoxDate) : null;

      }

   }

}

 
 

DefaultFormats:

namespace OurApp.Core.Infrastructure

{

   public static class DefaultFormats

   {

      public const string DatePickerDate = "yy-mm-dd";

      public const string JavaScriptDate = "yyyy-mm-dd";

      public const string TextBoxDate = "yyyy-MM-dd";

      public const string ListItemDelimiter = ", ";

      public const string CustomAttributeEmptySelectionText = "Any";

   }

}

 
 

Now our point of debate: Should this be done or should the DateTime just end up as a DateTime at the DTO for a view? Joel wondered how one might conditionally set a date to be bright red in the view if the date signified something a month overdue? Rafael suggested that for such a calculation, a separate Boolean value would also need to be kept on the DTO in lieu of making a calculation in the view off of a DateTime on the DTO.