Model passed to form in partialview returns with components (that were not null before calling form) being null on form post to controller - asp.net-core

Question

I have been trying to find out why submitting a form in my partialview makes some components of my model null. Just before calling the partialview, I have a model with count of AgainstWhoms and TimesPlaces each equal to one.
Even with a simplified partialview where only a column is added, on submitting to the controller, my AgainstWhoms and TimesPlaces collections are now null.
public class ComplaintViewModel
{
[Key]
public int Id { get; set; }
.........
public List<AgainstWhomViewModel> AgainstWhoms { get; set; }
public List<TimesPlacesViewModel> TimesPlaces { get; set; }
public List<WitnessesViewModel> Witnesses { get; set; }
}
public async Task<ActionResult> GetNewComplaint(int intComplainantId)
{
var complaint = new ComplaintViewModel
{
ComplainantId = intComplainantId,
StatusId = 1,
ReceivedDate = DateTime.Now,
AgainstWhoms = new List<AgainstWhomViewModel> { },
TimesPlaces = new List<TimesPlacesViewModel> { },
Witnesses = new List<WitnessesViewModel> { }
};
var newtime = new TimesPlacesViewModel { IncidentDate = DateTime.Today, IncidentLocation = "aaaaaaaaa" };
complaint.TimesPlaces.Add(newtime);
var complainee = new AgainstWhomViewModel { CountryId = 1, Email = "aaaaaaa#yahoo.com"};
complaint.AgainstWhoms.Add(complainee);
..................
return PartialView("_ComplaintFormModal", complaint);
}
Below is my simplified view.
#model ComplaintViewModel
<div>
<form id="Complaintform" asp-controller="Complaint" asp-action="RegisterComplaint" method="post">
<div class="form-row">
<div class="form-group col-lg-8 required">
<label asp-for="ComplaintTitle" class="control-label"></label>
<input type="text" class="form-control" required asp-for="ComplaintTitle">
<span asp-validation-for="ComplaintTitle" class="text-danger"></span>
</div>
</div>
<button type="submit" value="Submit">Submit</button>
</form>
</div>
In my controller post method, newComplaint.AgainstWhom and newComplaint.TimePlaces are now null, while other fields that do not belong to any of the linked lists are returned correctly:
[HttpPost]
public ActionResult RegisterComplaint(ComplaintViewModel newComplaint)
{
..............

Answer 1

You didn't render the TimesPlaces/AgainstWhoms so that data will lose since they are not in form collection .
If you want to edit the TimesPlaces/AgainstWhoms items , you can render like :
#for (int i = 0; i < Model.TimesPlaces.Count; i++)
{
<tr>
<td>
#Html.TextBoxFor(model => model.TimesPlaces[i].IncidentDate)
</td>
<td>
#Html.TextBoxFor(model => model.TimesPlaces[i].IncidentLocation)
</td>
</tr>
}
If you don't want to edit them , you can use hidden field :
#for (int i = 0; i < Model.TimesPlaces.Count; i++)
{
#Html.HiddenFor(model => model.TimesPlaces[i].IncidentDate)
#Html.HiddenFor(model => model.TimesPlaces[i].IncidentLocation)
}
But it's better to avoid that . If you don't want to edit them , i would prefer to query database with ID again for up-to-date records , and avoid posting large data in a request .