Save navigation property as null - asp.net-core

Question

I have a Job model and StatusOnHold model.
I added navigation property StatusOnHold in the Job model.
from some reason, when I'm saving the Job model with an empty StatusOnHold, I'm still getting value in the StatusOnHoldId in the Job model.
when StatusOnHold is empty, I'm trying to receive NULL value in the StatusOnHoldId in the Job model.
when StatusOnHold is not empty, I'm trying to get StatusOnHoldId and save the value in the StatusOnHold model (which it's working like that now).
Thank you so much.
Here is my Models...
public class StatusOnHoldViewModel
{
public int Id { get; set; }
public string Note { get; set; }
}
public class JobViewModel
{
[Key]
public int Id { get; set; }
public string JobNote { get; set; }
public JobStatus JobStatus { get; set; }
public CompanyViewModel Company { get; set; }
public CustomerViewModel Customer { get; set; }
public StatusOnHoldViewModel StatusOnHold { get; set; }
}
Here is the Controller...
public async Task<IActionResult> Create(JobViewModel jobViewModel)
{
if (ModelState.IsValid)
{
var job = _mapper.Map<Job>(jobViewModel);
var newjobId = await _jobRepository.AddAsync(job);
return RedirectToAction("details", new { id = newjobId });
}
return View();
}
And here is the view...
<div class="form-group row">
<label class="col-sm-2 col-form-label"></label>
<div class="col-sm-10">
<div class="m-1">On-Hold</div>
<textarea asp-for="StatusOnHold.Note" style="height:86px; min-height:86px" class="form-control" placeholder="Reason..."></textarea>
<span asp-validation-for="StatusOnHold.Note" class="text-danger"></span>
</div>
</div>

Answer 1

You don't have property for the StatusOnHoldViewModel the navigation property alone will not work.
So add
public int StatusOnHoldViewModelId { get; set; }
to your JobViewModel

Answer 2

StatusOnHoldId will not be empty and it always have data, if you do not write note in textarea, it will look like { "id":0,"note":null} on action for jobViewModel` ,this wll create a new record.
A workaround is that you could set StatusOnHold as null when note is null:
public async Task<IActionResult> Create(JobViewModel jobViewModel)
{
if (ModelState.IsValid)
{
if(jobViewModel.StatusOnHold.Note == null)
{
jobViewModel.StatusOnHold = null;
}
var job = _mapper.Map<Job>(jobViewModel);
var newjobId = await _jobRepository.AddAsync(job);
return RedirectToAction("details", new { id = newjobId });
}
return View();
}