asp.net mvc 3 - How do you exclude properties from binding when calling UpdateModel()?

Question

I have a view model sent to the edit action of my controller. The ViewModel contains references to EntityObjects. (yea i'm fine with it and don't need to want to duplicate all the entities properties in the viewmodel).

I instantiate the view model and then call UpdateModel. I get an error that a property is "null" which is fine since it is a related model. I am trying to exclude the property from being bound during model binding. On debugging it I see in the entity where the model binder is trying to set the value of the property to null.

Here is my edit action:

var model = new SimplifiedCompanyViewModel(id);

var excludeProperties = new string[] { 
   "Entity.RetainedEarningsAccount.AccountNo"
   ,"Property.DiscountEarnedAccount.ExpenseCodeValue"
   ,"Entity.EntityAlternate.EntityID"
   ,"Property.BankAccount.BankAccountID"
   ,"Entity.PLSummaryAccount.AccountNo"
   ,"Property.RefundBank.BankAccountID"
   ,"Company.Transmitter.TCC"
};

try
{
    UpdateModel<SimplifiedCompanyViewModel>(model, String.Empty, null, excludeProperties);

    if (ModelState.IsValid)
    {
       //db.SaveChanges();
    }
       return RedirectToAction("Index");
}
catch
{
    return View(model);
}

I have looked at a few other issues about specifying a "prefix" but I don't think that is the issue since I am telling it to bind to the viewmodel instance not just the entity object.

Am I excluding the properties correctly? Strange thing is is only seems to happen on this item. I suspect it may be an issue with the fact that there is actually no refund bank related to my entity. But I have other related items that don't exist and don't see the same issue.

More info... since I'm told me model isn't designed well.

The Company is related to a BankAccount. The Company view shows the currently related BankAccount.BankAccountId and there is a hidden field with the BankAccount.Key. I use jQueryUI autocomplete feature to provide a dropdown of bank account displaying the BankAccount.BankAccountId and when one is selected the jQuery code changes the hidden field to have the correct Key value. So, when this is posted I don't want the current bankaccounts BankAccountID modified, hence I want it to skip binding that field.

If I exclude BankAccountId in the model then on the BankAccount edit view the user would never be able to change the BankAccountId since it won't be bound. I'm not sure how this indicates a poor model design.

Answer 1

Use the Exclude property of the Bind attribute:

[Bind(Exclude="Id,SomeOtherProperty")]
public class SimplifiedCompanyViewModel
{
    public int Id { get; set; }

    // ...
}

This is part of the System.Web.Mvc namespace. It takes a comma-separated list of property names to exclude when binding.

Also you should consider using TryUpdateModel instead of UpdateModel. You can also just have the default model binder figure it out by passing it as an argument to the constructor:

public ActionResult Create([Bind(Exclude="Id")]SimplifiedCompanyViewModel model)
{
    // ...
}