MVC2 - How to obtain parent model (container) inside template

Question

I'm writing an MVC2 app using DataAnnotations. I have a following Model:

public class FooModel 
{
    [ScaffoldColumn("false")]
    public long FooId { get; set; }

    [UIHint("BarTemplate")]
    public DateTime? Bar { get; set;}
}

I want to create a custom display template for Bar. I have created following template:

<%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl<DateTime?>" %>

<div class="display-label">
    <span><%: Html.LabelForModel() %></span>
</div>
<div class="display-field">
    <span><%: Html.DisplayForModel()%></span>
    <%: Html.ActionLink("Some link", "Action", new { id = ??FooId?? }) %>
</div>

Now, my problem is that inside template for Bar I want to access another property from my model. I don't want to create a separate template for FooModel because than I will have to hardcode all other FooModel properties.

After a brief investigation with a debugger I can see that:

1. this.ViewData.ModelMetadata.ContainerType is FooModel (as expected)
2. this.ViewData.TemplateInfo has a non-public property VisitedObjects (of type System.Collections.Generic.HashSet<object>) which contains two elements: FooModel and DateTime?.

How can I get access to my FooModel? I don't want to hack my way around using Reflection.

Update:

I've accepted mootinator's answer as it looks to me as the best solution that allows type-safety. I've also upvoted Tx3's answer, as mootinator's answer builds upon it. Nevertheless, I think that there should be a better support form MVC in those kind of scenarios, which I believe are quite common in real world but missing from sample apps.

Answer 1

Sorry if this suggestion seems daft, I haven't tried it, but couldn't you do what Tx3 suggested without having to create a bunch of new classes by defining a generic class to reference whatever type of parent you want?

    public class FooModel 
    {
        [ScaffoldColumn("false")]
        public long FooId { get; set; }

        [UIHint("BarTemplate")]
        public ParentedDateTime<FooModel> Bar { get; set;}

        public FooModel()
        {
            Bar = new ParentedDateTime<FooModel>(this);
        }
    }


    public class ParentedDateTime<T>
    {
        public T Parent {get; set;}
        public DateTime? Babar {get; set; }

        public ParentedDateTime(T parent)
        {
            Parent = parent;
        }

}

You could expand that to encapsulate any old type with a <Parent, Child> typed generic, even.

That would also give you the benefit that your strongly typed template would be for

Inherits="System.Web.Mvc.ViewUserControl<ParentedDateTime<FooType>> thus you would not have to explicity name which template to use anywhere. This is more how things are intended to work.

Answer 2

Maybe you could create new class, let's say UserDateTime and it would contain nullable DateTime and rest of the information you need. Then you would use custom display template for UserDateTime and get access to information you require.

I realize that you might be looking for other kind of solution.

Answer 3

I think you may be better off extracting this functionality to an HtmlHelper call from the Parent View.

Something like RenderSpecialDateTime<TModel>(this HtmlHelper html, Expression<Func<TModel,DateTime?>> getPropertyExpression) would probably do the job.

Otherwise, you will have to do something like what Tx3 suggested. I upvoted his answer, but posted this as an alternative.

Answer 4

Couldn't you use the ViewData dictionary object in the controller and then grab that in the ViewUserControl? It wouldn't be strongly typed but...you could write a helper to do nothing if it's empty, and link to say the example login history page if it had a value.

Answer 5

It would appear that somewhere between MVC 5.0 and 5.2.2 a "Container" property was added on to the ModelMetadata class.

However, because all of the methods in a provider responsible for metadata creation (GetMetadataForProperty, Create etc) do not have container in their signature, the Container property is assigned only in certain cases (GetMetadataForProperties and GetMetadataFromProvider according to reflected code) and in my case was usually null.

So what I ended up doing is overriding the GetMetadataForProperty in a new metadata provider and setting it there:

public override ModelMetadata GetMetadataForProperty(Func<object> modelAccessor, Type containerType, string propertyName)
{
  var propMetaData = base.GetMetadataForProperty(modelAccessor, containerType, propertyName);
  Object container = modelAccessor.Target.GetType().GetField("container").GetValue(modelAccessor.Target);
  propMetaData.Container = container;
  return propMetaData;
}

I know this is reflection but it's fairly succinct. It would appear that MS is correcting this oversite so maybe it will be possible to replace the reflection code in the future.