ASP.NET MVC - Binding a Child Entity to the Model

Question

This one seems painfully obvious to me, but for some reason I can't get it working the way I want it to. Perhaps it isn't possible the way I am doing it, but that seems unlikely. This question may be somewhat related: http://stackoverflow.com/questions/1274855/asp-net-mvc-model-binding-related-entities-on-same-page.

I have an EditorTemplate to edit an entity with multiple related entity references. When the editor is rendered the user is given a drop down list to select related entities from, with the drop down list returning an ID as its value.

<%=Html.DropDownListFor(m => m.Entity.ID, ...)%>

When the request is sent the form value is named as expected: "Entity.ID", however my strongly typed Model defined as an action parameter doesn't have Entity.ID populated with the value passed in the request.

public ActionResult AddEntity(EntityWithChildEntities entityWithChildEntities) { }

I tried fiddling around with the Bind() attribute and specified Bind(Include = "Entity.ID") on the entityWithChildEntities, but that doesn't seem to work. I also tried Bind(Include = "Entity"), but that resulted in the ModelBinder attempting to bind a full "Entity" definition (not surprisingly).

Is there any way to get the default model binder to fill the child entity ID or will I need to add action parameters for each child entity's ID and then manually copy the values into the model definition?

Answer 1

Have you looked at AutoMapper? I agree that this shouldn't be required because the binding should work but...

I've had a little difficulty with using the Html.XYZFor helper and have reverted back to using the MVC 1.1 notation and it all works.

Answer 2

There's no DropDownListFor helper method that takes one parameter. The standard DropDownListFor method takes at least two parameters: the first is a lambda used to calculate the name of the select and the second is an IEnumerable<SelectListItem>:

<%= Html.DropDownListFor(m => m.Entity.ID, Model.EntitiesList) %>

Also how does the EntityWithChildEntities type looks like? It must be something like this:

public class EntityType
{
    public string ID { get; set; }
}

public class EntityWithChildEntities
{
    public EntityType Entity { get; set; }

    public IEnumerable<SelectListItem> EntitiesList
    {
        get 
        {
            return new[]
            {
                new SelectListItem { Value = "1", Text = "foo" },
                new SelectListItem { Value = "2", Text = "bar" },
            }
        }
    }
}