Question

I’m having difficulties to understand what happens when ModelState is not valid (EF4.1, database first).

The following code shows creating a task for a project.

Whenever the model is valid, everything is OK, but when model is not valid, I got an exception that no parameter has been passed to model (however the route is correct and everything should be ok).
What am I doing wrong?

 //
    // POST: /Task/Create
    [Authorize()]
    [HttpPost]
    public ActionResult Create(int projectId, CPIO_Tasks task)
    {
        ViewBag.projId = projectId;

        try
        {            
            task.t_p_id = projectId;
            if (ModelState.IsValid)
            {

                db.CPIO_Tasks.AddObject(task);
                db.SaveChanges();
                return RedirectToAction("Details", "Projects", new { id = task.t_p_id });
            }

        }
        catch (DataException ex)
        {
            ModelState.AddModelError("Nieudane dodanie:", ex.ToString());
        }
        return RedirectToAction("Create", "Task", new {id = projectId});
    }

The parameters dictionary contains a null entry for parameter ‘projectId’ of non-nullable type ‘System.Int32’ for method ‘System.Web.Mvc.ActionResult Create(Int32)’ in ‘CPIO_WebUI.Controllers.TaskController’. An optional parameter must be a reference type, a nullable type, or be declared as an optional parameter.
Parameter name: parameters

The path with redirect id correct: localhost:11314/Task/Create/2.

Thanks in advance for any help

Anna

Answer 1

As the error message says, for you to not pass a projectId to your method, you’d need to make your method look like this:

public ActionResult Create(int? projectId, CPIO_Tasks task)
{
    // .....
}

What this does is use a Nullable<int> for the parameter taking the value type (which doesn’t allow null) and making it a reference type to allow null. That way you can pass a null value without running into this exception.