MVC 2 UpdateModel - how does it work?

Question

I ask because I cannot get this code to work. I get an exception; "The model of type 'ITOC.WebUI.Models.Contract' could not be updated." Which does not seem very helpful.

** EDIT ** The above exception has been resolved because of a spelling mistake in the prefix, a classic "Magic String". Now the problem is that NOTHING GETS UPDATED! ** END EDIT **

I have to admit I am not clear how UpdateModel works, and I am not clear how the prefix works. The viewmodel is specified in the webpage;

<%@ Page Title="" Language="C#" MasterPageFile="~/Views/Shared/Site.Master" 
Inherits="System.Web.Mvc.ViewPage<ITOC.WebUI.Models.ContractViewModel>" %>

and the ViewModelClass is

public class ContractViewModel
{
    //private ITOCEntities db = new ITOCEntities();
    public Contract contract { get; set; }
    public IList<ContractType> contractTypes { get; set; }
    public IEnumerable<SelectListItem> contractTypesSelectList
    {
        get
        {
            return this.contractTypes.Select(item => new SelectListItem
            {
                Text = item.ContractType1,
                Value = item.ContractTypeId.ToString()
            });
        }
    }


    public Contact clientContact { get; set; }
    public Contact contractAdministratorContact { get; set; }

    public ContractViewModel()
    {
        using (var db = new ITOCEntities())
        {
            this.contractTypes = db.ContractTypes.ToList();

            this.clientContact = new Contact();
            this.contractAdministratorContact = new Contact();
            this.clientContact.ContactTypeId =
                db.ContactTypes.Where(x => x.ContactType1 == "Client").SingleOrDefault().ContactTypeId;
            this.contractAdministratorContact.ContactTypeId =
                db.ContactTypes.Where(x => x.ContactType1 == "CA").SingleOrDefault().ContactTypeId;
        }
    }
    public ContractViewModel(int contractId)
    {
        using (var db = new ITOCEntities())
        {
            this.contractTypes = db.ContractTypes.ToList();
            this.contract = db.Contracts.Where(x => x.ContractId == contractId).SingleOrDefault();
            this.clientContact = 
                db.Contacts.Where(x => x.ContactId == this.contract.ClientContactId).SingleOrDefault();
            this.contractAdministratorContact =
                db.Contacts.Where(x => x.ContactId == this.contract.ContractAdministratorContactId).SingleOrDefault(); 

        }
    }
}

---

The Controller is;

[Authorize(Roles = "Inputter")]
[HttpPost]
public ActionResult Edit(int contractId, FormCollection formValues)
{
    if (ModelState.IsValid)
    {
        using (var db = new ITOCEntities())
        {
            var contract = db.Contracts.Single(x => x.ContractId == contractId);
            string letter = contract.ContractNo_Letter;

            UpdateModel(contract, "Contracts");

            var clientContact = db.Contacts.Single(x => x.ContactId == contract.ClientContactId);
            UpdateModel(clientContact, "Contact");
            var contractAdministrationContact = 
                db.Contacts.Single(x => x.ContactId == contract.ContractAdministratorContactId);
            UpdateModel(contractAdministrationContact, "Contact");
            db.SaveChanges();
        }

        return RedirectToAction("List");
    }
    return View();
}

Answer 1

try using TryUpdateModel in an if/ else statement

if (TryUpdateModel(contract))
{
    // save changes
}
else
{
    // handle
}

TryUpdateModel and UpdateModel are intended to be used to merge an object with a posted model object.

Updates the specified model instance using values from the controller's current value provider.

• http://msdn.microsoft.com/en-us/library/system.web.mvc.controller.tryupdatemodel.aspx

Try reading this post about these two methods.

---

try changing your Post Action Method to match your Model Object

[Authorize(Roles = "Inputter")]
[HttpPost]
public ActionResult Edit(ContractViewModel model)
{
    //
}

if the id's on your form match to the properties of your ContractViewModel object then model will post with those values

Answer 2

A few things I noticed right off:

1. You don't have a ViewModel specified in your view. This line here means a View with no type specific model:

   <%@ Page Title="" Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="System.Web.Mvc.ViewPage" %>

2. Without seeing the view, we can't be sure what you're trying to bind to here, or even if you should be using a prefix.

3. You're not actually passing in the FormValues collection into UpdateModel. Try:UpdateModel(contract, "Contract", formValues)

Answer 3

To see what failed look at your Controller.ModelState entries. That will tell you what failed to bind. In my experience its usually a datatype mismatch.

---

1 and 3 of CubanX's answer don't really have any impact on ModelBinding errors. 2 can be ignored because if your getting a bind error you know its probably binding and probably don't have to worry about the Prefix.