EF Core ModelSate Invalid because form is passing foreign key name and value attributes - asp.net-mvc

Question

Very new to MVC Core and C# and just as I think I'm getting the hang of something there's a new curve ball. I have a form which is based on a model which has a foreign key. When I submit the form to the controller the modelState is invalid because the form is passing something back which isn't in the model it is based on. Here is the model:
public partial class Agreement
{
public Agreement()
{
AgreementAmendments = new HashSet<AgreementAmendment>();
Bundles = new HashSet<Bundle>();
Invoices = new HashSet<Invoice>();
}
public int Id { get; set; }
public int OrgId { get; set; }
public string AgreementNumber { get; set; } = null!;
public string? IrespondReference { get; set; }
public string? DocumentLink { get; set; }
public virtual Organization Org { get; set; }
public virtual ICollection<AgreementAmendment> AgreementAmendments { get; set; }
public virtual ICollection<Bundle> Bundles { get; set; }
public virtual ICollection<Invoice> Invoices { get; set; }
}
This is the Get Create Action Method:
public IActionResult Create()
{
ViewData["OrgId"] = new SelectList(_context.Organizations, "Id", "ShortName");
return View();
}
This is the form:
<div class="row">
<div class="col-md-4">
<form asp-action="Create">
<div asp-validation-summary="ModelOnly" class="text-danger"></div>
<div class="form-group">
<label asp-for="OrgId" class="control-label">Organization</label>
<select asp-for="OrgId" class ="form-control" asp-items="ViewBag.OrgId"></select>
</div>
<div class="form-group">
<label asp-for="AgreementNumber" class="control-label">Agreement Number</label>
<input asp-for="AgreementNumber" class="form-control" />
<span asp-validation-for="AgreementNumber" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="IrespondReference" class="control-label">Internal Reference</label>
<input asp-for="IrespondReference" class="form-control" />
<span asp-validation-for="IrespondReference" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="DocumentLink" class="control-label">Document Link</label>
<input asp-for="DocumentLink" class="form-control" />
<span asp-validation-for="DocumentLink" class="text-danger"></span>
</div>
<div class="form-group">
<input type="submit" value="Create" class="btn btn-primary" />
</div>
</form>
</div>
</div>
And this is the HttpPost Create Action Method:
[HttpPost]
[ValidateAntiForgeryToken]
public async Task<IActionResult> Create([Bind("OrgId,AgreementNumber,IrespondReference,DocumentLink")] Agreement agreement)
{
if (ModelState.IsValid)
{
_context.Add(agreement);
await _context.SaveChangesAsync();
return RedirectToAction(nameof(Index));
}
ViewData["OrgId"] = new SelectList(_context.Organizations, "Id", "Id", agreement.OrgId);
return View();
}
When I look at the results of the ModelState it shows an error with the Org Key but as far as I can see the form should just be returning the OrgId as per the model. Can someone please let me know where I am going wrong.

Answer 1

Created a View Model for Agreements to handle the form input and then passed that to the base Agreement Model which seems like unnecessary work. Why can't EF Core handle this stuff without having to constantly build View Models just because there is a foreign key?
Anyway, this is the final HttpPost code for others who run into the same issue:
[HttpPost]
[ValidateAntiForgeryToken]
public async Task<IActionResult> Create(AgreementWriteViewModel newagreement)
{
if (ModelState.IsValid)
{
var model = new Agreement
{
OrgId = newagreement.OrgId,
AgreementNumber = newagreement.AgreementNumber,
IrespondReference = newagreement.IrespondReference,
DocumentLink = newagreement.DocumentLink,
};
_context.Add(model);
await _context.SaveChangesAsync();
return RedirectToAction(nameof(Index));
}
ViewData["OrgId"] = new SelectList(_context.Organizations, "Id", "ShortName", newagreement.OrgId);
return View();
}