The ASP.NET controller is unable to process a null array

I am developing an application using Angular.js and ASP.NET. Here is the model I have defined:

public class Dealer : EntityBase
{
    ...
    public virtual List<DealerDefinedService> DealerDefinedServices { get; set; }
    public virtual List<DealerDefinedServicesDiscount> DealerDefinedServicesDiscounts { get; set; }
    ...
}

I also have a controller that can handle this model:

[HttpPost]
public ActionResult Edit(Dealer model)
{
    if (ModelState.IsValid)
    {
        dealerService.EditDealer(model);

        return RedirectToAction("Index");
    }
    return View("Create", model);
}

When trying to send an object from my Angular.js controller with these properties:

{
  "DealerDefinedServices": [
    {
      ...
    }
  ],
  "DealerDefinedServicesDiscounts": [
    {
      ...
    }
  ]
}

The issue arises when both "DealerDefinedServices" and "DealerDefinedServicesDiscounts" parameters are set—only one of them gets recognized by the ASP.NET controller while the other becomes null. After hours of troubleshooting, I was able to fix it by renaming one of the parameters as I suspected the problem might be due to their similar names. What could be causing the controller to overlook one parameter when they share similar names?

Answer №1

Perhaps the issue lies with the FormValueProvider within the default model binder, as it may be getting confused. The ContainsPrefix(String) method could be the culprit in this case. One suggestion would be to rename the second parameter to

Dealer1DefinedServicesDiscounts

and then change it to

DealerDefinedServices1Discounts

The former should function correctly while the latter might result in the null problem.

Cause of this behavior

The default model binder uses a FormValueProvider to extract the field's value from the request and assign it to your Dealer model. The FormValueProvider relies on the ContainsPrefix method to locate the field in the request, which in this scenario is your $scope.model object. It is possible that ContainsPrefix is providing incorrect information to the model binder because the prefix DealerDefinedServices is common to both properties in your model.

I do not possess enough knowledge about model binders to explain the sequence of code execution and why the model binder sets one property to null.

If you have already attempted changing the property names to avoid shared prefixes, it should resolve this issue.

An alternative solution could involve using a WebAPI instead of an action method in MVC. The model binders for Action methods are designed to handle form objects (hence the name FormValueProvider), whereas what you are passing essentially behaves as a JSON/JavaScript object. A WebAPI model binder might prove more effective in binding it. Please note: I have not tested this, so WebAPI could potentially face similar challenges.

Answer №2

There seems to be a known issue with MVC4 that users should look out for. Details can be found at this link

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