EditorFor on nullable DateTime - "Nullable object must have a value."

Question

I am attempting to display a form that allows a user to input a new assignment for a person. I'm using a DateTime.cshtml EditorTemplate to handle DateTime values for the assignment. The non-nullable DateTime works fine. The nullable DateTime causes an "InvalidOperationException: Nullable object must have a value."

I have a simple viewmodel that looks like this:

AssignmentViewModel.cs:

public Person Person { get; set; }
public Assignment NewAssignment { get; set; }

Assignment.cs contains:

public DateTime AssignmentStartDate { get; set; }
public DateTime? AssignmentEndDate { get; set; }

My AssignmentController Create() method looks like:

public ViewResult Create(int personId)
{
    Person person = personRepository.GetPersonById(personId);
    var newAssignment = new AssignmentViewModel { Person = person, NewAssignment = new Assignment() };
    return View(newAssignment);
}

My Create.cshtml view looks like this:

@model AssignmentViewModel

@using (Html.BeginForm("Create", "Assignment"))
{
    @Html.Hidden("NewAssignment.PersonId", Model.Person.PersonId)
    @Html.LabelFor(x => x.NewAssignment.AssignmentStartDate):
    @Html.EditorFor(x => x.NewAssignment.AssignmentStartDate.Date, new { cssClass = "datePicker" })
    <br />
    @Html.LabelFor(x => x.NewAssignment.AssignmentEndDate):
    @Html.EditorFor(x => x.NewAssignment.AssignmentEndDate.Value.Date, new { cssClass = "datePicker" })
    <br />
    <input type="submit" value="Send />
}

My DateTime.cshtml EditorTemplate looks like:

@model DateTime?

@{
    String modelValue = "";
    if (Model.HasValue)
    {
        if (Model.Value != DateTime.MinValue)
        {
            modelValue = Model.Value.ToShortDateString();
        }
    }
}

@Html.TextBox("", modelValue, new { @class = "datePicker" })

When I attempt to load the Create view, I get the exception mentioned above on the line "@Html.EditorFor(x => x.NewAssignment.AssignmentEndDate.Value)".

You may be wondering why I'm passing in AssignmentEndDate.Value.Date instead of just passing in AssignmentEndDate; the reason is because I'm trying to get to the point where I'm splitting DateTime into Date and a TimeOfDay field and recombine them with a DateTimeModelBinder. I am using a similar technique to the one shown here and here.

I -can- bypass the error, by changing my controller Create() method to instantiate the ViewModel with AssignmentEndDate set to DateTime.MinValue, but this seems completely wrong for a nullable DateTime:

var newAssignment = new AssignmentViewModel 
                        { 
                            Person = person, 
                            NewAssignment = new Assignment { AssignmentEndDate = DateTime.MinValue } 
                        };

Something strange happens after I "bypass" the error by supplying a value for the nullable DateTime; the un-required nullable DateTime property (AssignmentEndDate.Date) fails client side validation. Trying to submit the form highlights the field in red.

How can I handle this correctly?

Answer 1

The problem is that you're trying to retrieve the AssignmentEndDate.Value.Date, but AssignmentEndDate is null, which results in this error.

Since your editor template accepts a DateTime?, you should just pass along the AssignmentEndDate. In other words, remove the .Value.Date from the view:

@Html.EditorFor(x => x.NewAssignment.AssignmentEndDate, new { cssClass = "datePicker" })

Since your editor template is using ToShortDateString(), there's no need to "truncate" the time from the date at all.

Update

Regarding your desire to have separate "Date" and "Time" editors:

You can do this 2 ways.

1 - Your current DateTime? editor renders a field for the Model.Value.Date, so you could simply extend this to also render a field for the Model.Value.TimeOfDay. Example:

@{
  DateTime? modelDate = (Model == null) ? (DateTime?)null : Model.Value.Date;
  TimeSpan? modelTime = (Model == null) ? (TimeSpan?)null : Model.Value.TimeOfDay;
}
@Html.TextBox(..., modelDate, new{@class="datePicker"})
@Html.TextBox(..., modelTime, new{@class="timePicker"})

2 - You could split the above functionality into 2 separate editors, "DateOnly" and "TimeOnly". Then, update your view to call both editors:

@Html.EditorFor(x => x.NewAssignment.AssignmentEndDate, "DateOnly")
@Html.EditorFor(x => x.NewAssignment.AssignmentEndDate, "TimeOnly")

The choice is up to you, and whether you want to keep the Date and Time parts separate or together, but this is how I'd go about solving this problem.