Question

I have two view models, one aggregating a collection of the other:

class Parent 
{
   public string Key { get; set; }
   public IList<Child> Children { get; set; }
}

class Child
{
   public string Key { get; set; }

   [Required, Remote("VerifyNameUnique", "Parent", AdditionalFields = "Key", ErrorMessage = "The name must be unique.")]
   public string Name { get; set; }
}

I have a controller action

public ActionResult VerifyNameUnique(string key, string name)
{
    var result = // ... verify uniqueness
    return Json(result, JsonRequestBehavior.AllowGet);
}

And a view:

@model Parent
@Html.HiddenFor(m => m.Key)
@for(var i=0; i<Model.Children; i++)
{
   @Html.HiddenFor (m => m.Children[i].Key)
   @Html.LabelFor(m => m.Children[i].Name)
   @Html.EditorFor (m => m.Children[i].Name)
}

When my Parent/Child editor template calls the action to validate any of the Name fields, it sends a querystring ?Children[0].Key=abc&Children[0].Name=Fred, where 0 is the index i of the child just edited.

That doesn’t bind to the parameters of VerifyNameUnique because of the prefix. I have tried using BindAttribute with a prefix set, but the prefix varies by the value of i.

Writing a custom model binder is an option but seems like overkill right now for this simple scenario. Is there anything nicer I can do?

Answer 1

This simply is not supported. So you will have to either write a custom model binder or a custom Remote validation attribute. This being said, what you are trying to achieve is probably not a very good idea because if the user clicks on the submit button an AJAX request will be sent for every field in the collection which is not very efficient. I would probably go with a custom remote validation field directly on the collection property on the parent in order to validate everything with a single roundtrip to the server.