How can I overwrite an existing map in Automapper

This is driving me nuts... I have been trying to pass a variable to a custom resolver, but it seems impossible to do.

I am currently using the following approach, but the value that is passed to the Custom Resolvers constructor is always an empty string "" even though I specifically register a new mapping to overwrite the existing one (See controller)

Custom Resolver

public class DueDateResolver :  ValueResolver<Task, string>
{

    public string DateFormat = "MMM dd, @ h:mm tt";


    public DueDateResolver(string dateFormat)
    {
        // If no date format is pa开发者_开发知识库ssed use the default
        if (!String.IsNullOrEmpty(dateFormat))
        {
            DateFormat = dateFormat;
        }
    }
}

Controller

// <summary>
    /// Ajax Method for filtering tasks by Date Range
    /// </summary>
    /// <param name="dateFilter">The date filter label ["Day", "Week", "Month", "All", "Last 30 Days"]</param>
    /// <returns>List of task objects</returns>
    [HttpGet]
    public JsonResult GetTasksByDateRange(DateFilters dateFilter)
    {
        RegisterMaps.RegisterTaskViewModel(dateFilter.ToString());

        List<Task> tasks = taskService.GetFilteredTasksByDate(dateFilter, "chobojunk@gmail.com");
        List<TaskTableViewModel> viewModelList = Mapper.Map<List<Task>, List<TaskTableViewModel>>(tasks);

        return Json(viewModelList, JsonRequestBehavior.AllowGet);
    }

Mappings

The Register() method is done at the global.asa level. The other method above is called in my controller.

/// <summary>
    /// Special case where I need to pass in a parameter
    /// </summary>
    public static void RegisterTaskViewModel(string dateFilter)
    {
        Mapper.CreateMap<Task, TaskTableViewModel>().ForMember(dest => dest.DueDate,
                                                     opt => opt.ResolveUsing<DueDateResolver>().ConstructedBy(() => new DueDateResolver(dateFilter)));
    }


    public static void Register()
    {
        Mapper.CreateMap<Task, TaskTableViewModel>().ForMember(dest => dest.DueDate,
                                                  opt => opt.ResolveUsing<DueDateResolver>().ConstructedBy(() => new DueDateResolver("")));
}

I would create the mapping once then leave it alone. Create a context object with your resolver parameter, use DI/IoC to inject it into the resolver, and update it from the controller before executing the mapper.