In the contact creation I want to assign a customer or supplier from a dropdown - validation

Question

I have two problems.
1. Problem: When I add my selection to the razor page all required fields validation from the model do not work anymore.
Validation from model without selection
No Validation when I add my selection
When dropdown are in the Razor html no validation works and it crashes with NULL Values which I want to prevent. Like it is without select options.
Why is that?
2. Problem: When I select a customer from my drop down (CustomerDropDown.CusId) I would like to fill the ID into my ID field of contacts (contacts.CustomerId). How can I reach the selected value from dropdown and post it to my contact contacts.CustomerId?
== c# code ==
using System;
using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;
using Microsoft.EntityFrameworkCore;
using Microsoft.AspNetCore.Mvc.Rendering;
using WorkCollaboration.Data;
using WorkCollaboration.Models;
namespace WorkCollaboration.Pages.Contacts
{
public class CreateModel : PageModel
{
private readonly WorkCollaboration.Data.WorkCollaborationContext _context;
public CreateModel(WorkCollaboration.Data.WorkCollaborationContext context)
{
_context = context;
}
public async Task<IActionResult> OnGetAsync()
{
CustomerDropDownDisp = await _context.CustomerDropDown.ToListAsync(); // Added for DropDown
SupplierDropDownDisp = await _context.SupplierDropDown.ToListAsync(); // Added for DropDown
return Page();
}
[BindProperty]
public Contact Contact { get; set; }
public IEnumerable<CustomerDropDown> CustomerDropDownDisp { get; set; }
public IEnumerable<SupplierDropDown> SupplierDropDownDisp { get; set; }
// To protect from overposting attacks, enable the specific properties you want to bind to, for
// more details, see https://aka.ms/RazorPagesCRUD.
public async Task<IActionResult> OnPostAsync()
{
if (!ModelState.IsValid)
{
return Page();
}
_context.Contact.Add(Contact);
await _context.SaveChangesAsync();
return RedirectToPage("/ContactsOverview/Index");
}
}
}
== Razor Page Code ==
#page
#using WorkCollaboration.Models
#model WorkCollaboration.Pages.Contacts.CreateModel
#{
ViewData["Title"] = "Create";
ViewData["RandomId"] = Guid.NewGuid().GetHashCode();
}
<h1>Create</h1>
<h4>Contact</h4>
<p>
<a asp-page="/ContactsOverview/Index">Back to Index</a>
</p>
<hr />
<div class="row">
<div class="col-md-4">
<form method="post">
<div asp-validation-summary="ModelOnly" class="text-danger"></div>
<div class="form-group">
<label asp-for="Contact.ContactId" class="control-label"></label>
<input asp-for="Contact.ContactId" value='#ViewData["RandomId"]' readonly="readonly" class="form-control" />
<span asp-validation-for="Contact.ContactId" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Contact.LastName" class="control-label"></label>
<input asp-for="Contact.LastName" class="form-control" />
<span asp-validation-for="Contact.LastName" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Contact.FirstName" class="control-label"></label>
<input asp-for="Contact.FirstName" class="form-control" />
<span asp-validation-for="Contact.FirstName" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Contact.CustomerId" class="control-label"></label>
</div>
<select id="CusId" asp-for="CustomerDropDownDisp" asp-items="#(new SelectList(Model.CustomerDropDownDisp,"CusId","CusName"))">
<option value="">--Choose Customer--</option>
<option value="1" selected>None</option>>
</select>
<div class="form-group">
<input asp-for="Contact.CustomerId" class="form-control" />
<span asp-validation-for="Contact.CustomerId" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Contact.SupplierId" class="control-label"></label>
</div>
<select id="SupId" asp-for="SupplierDropDownDisp" asp-items="#(new SelectList(Model.SupplierDropDownDisp,"SupId","SupName"))">
<option value="">--Choose Supplier--</option>
<option value="1" selected>None</option>>
</select>
<div class="form-group">
<input asp-for="Contact.SupplierId" class="form-control" />
<span asp-validation-for="Contact.SupplierId" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Contact.PrivateStreet" class="control-label"></label>
<input asp-for="Contact.PrivateStreet" class="form-control" />
<span asp-validation-for="Contact.PrivateStreet" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Contact.PrivateStreetNo" class="control-label"></label>
<input asp-for="Contact.PrivateStreetNo" class="form-control" />
<span asp-validation-for="Contact.PrivateStreetNo" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Contact.PrivateStreetAdditionalInfo" class="control-label"></label>
<input asp-for="Contact.PrivateStreetAdditionalInfo" class="form-control" />
<span asp-validation-for="Contact.PrivateStreetAdditionalInfo" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Contact.PrivateZip" class="control-label"></label>
<input asp-for="Contact.PrivateZip" class="form-control" />
<span asp-validation-for="Contact.PrivateZip" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Contact.PrivateTown" class="control-label"></label>
<input asp-for="Contact.PrivateTown" class="form-control" />
<span asp-validation-for="Contact.PrivateTown" class="text-danger"></span>
</div>
<div class="form-group">
#Html.LabelFor(model => model.Contact.PrivateCountry, htmlAttributes: new { #class = "form-group" })
<div class="form-group">
#Html.DropDownListFor(model => model.Contact.PrivateCountry, new List<SelectListItem>
{
new SelectListItem {Text = "CH", Value = "CH", Selected = true },
new SelectListItem {Text = "D", Value = "D" },
new SelectListItem {Text = "FL", Value = "FL" },
}, new { #class = "form-control" })
#Html.ValidationMessageFor(model => model.Contact.PrivateCountry, "", new { #class = "text-danger" })
</div>
</div>
<div class="form-group">
<label asp-for="Contact.PrivatePhone" class="control-label"></label>
<input asp-for="Contact.PrivatePhone" class="form-control" />
<span asp-validation-for="Contact.PrivatePhone" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Contact.BusinessPhone" class="control-label"></label>
<input asp-for="Contact.BusinessPhone" class="form-control" />
<span asp-validation-for="Contact.BusinessPhone" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Contact.MobilePhone" class="control-label"></label>
<input asp-for="Contact.MobilePhone" class="form-control" />
<span asp-validation-for="Contact.MobilePhone" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Contact.Mail" class="control-label"></label>
<input asp-for="Contact.Mail" class="form-control" />
<span asp-validation-for="Contact.Mail" class="text-danger"></span>
</div>
<div class="form-group">
<input type="submit" value="Create" class="btn btn-primary" />
Back to List
</div>
</form>
</div>
</div>
Thank you for your help on how to get selected value (dropdown) to the corresponding contacts Id field.

Answer 1

Here is a demo:
<div class="row">
<div class="col-md-4">
<form method="post">
<div asp-validation-summary="ModelOnly" class="text-danger"></div>
<div class="form-group">
<label asp-for="Contact.ContactId" class="control-label"></label>
<input asp-for="Contact.ContactId" value='#ViewData["RandomId"]' readonly="readonly" class="form-control" />
<span asp-validation-for="Contact.ContactId" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Contact.LastName" class="control-label"></label>
<input asp-for="Contact.LastName" class="form-control" />
<span asp-validation-for="Contact.LastName" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Contact.FirstName" class="control-label"></label>
<input asp-for="Contact.FirstName" class="form-control" />
<span asp-validation-for="Contact.FirstName" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Contact.CustomerId" class="control-label"></label>
</div>
<select id="CusId" asp-for="CustomerDropDownDisp" asp-items="#(new SelectList(Model.CustomerDropDownDisp,"CusId","CusName"))">
<option value="">--Choose Customer--</option>
<option value="1" selected>None</option>>
</select>
<div class="form-group">
<input asp-for="Contact.CustomerId" class="form-control" />
<span asp-validation-for="Contact.CustomerId" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Contact.SupplierId" class="control-label"></label>
</div>
<select id="SupId" asp-for="SupplierDropDownDisp" asp-items="#(new SelectList(Model.SupplierDropDownDisp,"SupId","SupName"))">
<option value="">--Choose Supplier--</option>
<option value="1" selected>None</option>>
</select>
<div class="form-group">
<input asp-for="Contact.SupplierId" class="form-control" />
<span asp-validation-for="Contact.SupplierId" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Contact.PrivateStreet" class="control-label"></label>
<input asp-for="Contact.PrivateStreet" class="form-control" />
<span asp-validation-for="Contact.PrivateStreet" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Contact.PrivateStreetNo" class="control-label"></label>
<input asp-for="Contact.PrivateStreetNo" class="form-control" />
<span asp-validation-for="Contact.PrivateStreetNo" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Contact.PrivateStreetAdditionalInfo" class="control-label"></label>
<input asp-for="Contact.PrivateStreetAdditionalInfo" class="form-control" />
<span asp-validation-for="Contact.PrivateStreetAdditionalInfo" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Contact.PrivateZip" class="control-label"></label>
<input asp-for="Contact.PrivateZip" class="form-control" />
<span asp-validation-for="Contact.PrivateZip" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Contact.PrivateTown" class="control-label"></label>
<input asp-for="Contact.PrivateTown" class="form-control" />
<span asp-validation-for="Contact.PrivateTown" class="text-danger"></span>
</div>
<div class="form-group">
#Html.LabelFor(model => model.Contact.PrivateCountry, htmlAttributes: new { #class = "form-group" })
<div class="form-group">
#Html.DropDownListFor(model => model.Contact.PrivateCountry, new List<SelectListItem>
{
new SelectListItem {Text = "CH", Value = "CH", Selected = true },
new SelectListItem {Text = "D", Value = "D" },
new SelectListItem {Text = "FL", Value = "FL" },
}, new { #class = "form-control" })
#Html.ValidationMessageFor(model => model.Contact.PrivateCountry, "", new { #class = "text-danger" })
</div>
</div>
<div class="form-group">
<label asp-for="Contact.PrivatePhone" class="control-label"></label>
<input asp-for="Contact.PrivatePhone" class="form-control" />
<span asp-validation-for="Contact.PrivatePhone" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Contact.BusinessPhone" class="control-label"></label>
<input asp-for="Contact.BusinessPhone" class="form-control" />
<span asp-validation-for="Contact.BusinessPhone" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Contact.MobilePhone" class="control-label"></label>
<input asp-for="Contact.MobilePhone" class="form-control" />
<span asp-validation-for="Contact.MobilePhone" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Contact.Mail" class="control-label"></label>
<input asp-for="Contact.Mail" class="form-control" />
<span asp-validation-for="Contact.Mail" class="text-danger"></span>
</div>
<div class="form-group">
<input type="submit" value="Create" class="btn btn-primary" />
Back to List
</div>
</form>
</div>
</div>
<script src="~/lib/jquery/dist/jquery.min.js"></script>
<script src="~/lib/jquery-validation/dist/jquery.validate.min.js"></script>
<script src="~/lib/jquery-validation-unobtrusive/jquery.validate.unobtrusive.min.js"></script>
<script>
$("#CusId").on("change", function () {
$("#Contact_CustomerId").val($("#SupId").val());
});
$("#SupId").on("change", function () {
$("#Contact_SupplierId").val($("#SupId").val());
});
</script>
result: