Question

Consider an HTML form built in the following way:

        <select name="schoolType">
            @foreach (SchoolType schoolType in Model.SchoolTypes)
            {
                <option value="@schoolType.Id">@schoolType.Name</option>
            }
        </select>

Now, SchoolType is a model class. It’s designed in my EDMX for Entity Framework.

In the above scenario, right now, my action method looks like this:

    public ActionResult CreateSchool(int schoolType)
    {
        ...
        SchoolType myType = container.SchoolTypeSet.FirstOrDefault(t => t.Id == schoolType);
        ...
    }

Would it be possible to program some kind of helper so that MVC would automatically know to convert the integer into a Model class with that ID, like the following action method signature?

    public ActionResult CreateSchool(SchoolType schoolType)
    {
        ...
    }

Answer 1

You can use a ModelBinder to accomplish this:

public ActionResult CreateSchool([ModelBinder(typeof(SchoolTypeBinder))] SchoolType schoolType)
{
    ...
}

Where your Model Binder looks like:

public class SchoolTypeBinder : IModelBinder
{
    public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
    {
        SchoolType output = null;

        int id;
        ValueProviderResult parameter = bindingContext.ValueProvider.GetValue("id");
        if (parameter != null)
        {
            id = (int)parameter.ConvertTo(typeof(int));
            output = container.SchoolTypeSet.FirstOrDefault(t => t.Id == id);
        }
        return output;
    }
}

You can also associate binders with types globally at startup:

protected void Application_Start()
{
    ...
    ModelBinders.Binders.Add(typeof(SchoolType), new SchoolTypeBinder());
}

resulting in the nice, clean action you requested:

public ActionResult CreateSchool(SchoolType schoolType)
{
    ...
}