akd
akd

Reputation: 6758

Best way to get table header names in MVC 4

I'm trying to display a list of objects in a table. I can iterate over each individual item to find it's value (using an for loop or a DisplayTemplate), but how do I abitriarily pick one to display headers for the whole group.

Here's an simplified example:

Model:

public class ClientViewModel
{
    public int Id { get; set; }
    public List<ClientDetail> Details { get; set; }
}
public class ClientDetail
{
    [Display(Name="Client Number")]
    public int ClientNumber { get; set; }
    [Display(Name = "Client Forname")]
    public string Forname { get; set; }
    [Display(Name = "Client Surname")]
    public string Surname { get; set; }
}

View

@model MyApp.ViewModel.ClientViewModel

@{ var dummyDetail = Model.Details.FirstOrDefault(); }

<table>
    <thead>
        <tr>
            <th>@Html.DisplayNameFor(model => dummyDetail.ClientNumber)</th>
            <th>@Html.DisplayNameFor(model => dummyDetail.Forname)</th>
            <th>@Html.DisplayNameFor(model => dummyDetail.Surname)</th>
        </tr>
    </thead>
    <tbody>
        @for (int i = 0; i < Model.Details.Count; i++)
        {
              <tr>
                <td>@Html.DisplayFor(model => model.Details[i].ClientNumber)</td>
                <td>@Html.DisplayFor(model => model.Details[i].Forname)</td>
                <td>@Html.DisplayFor(model => model.Details[i].Surname)</td>
            </tr>
        }
    </tbody>
</table>

Notice: I'm using var dummyDetail = Model.Details.FirstOrDefault(); to get a single item whose properties I can access in DisplayNameFor.

Upvotes: 6

Views: 11690

Answers (2)

KyleMit
KyleMit

Reputation: 29909

The Problem

As Thomas pointed out, Chris's answer works in some cases, but runs into trouble when using a ViewModel because the nested properties don't enjoy the same automatic resolution. This works if your model type is IEnumerable<Type>, because the DisplayNameFor lambda can still access properties on the model itself:

Model vs Enum<Model>

However, if the ClientDetail collection is nested inside of a ViewModel, we can't get to the item properties from the collection itself:

Collection inside ViewModel

The Solution

As pointed out in DisplayNameFor() From List in Model, your solution is actually perfectly fine. This won't cause any issues if the collection is null because the lambda passed into DisplayNameFor is never actually executed. It's only uses it as an expression tree to identify the type of object.

So any of the following will work just fine:

@Html.DisplayNameFor(model => model.Details[0].ClientNumber)

@Html.DisplayNameFor(dummy => Model.Details.FirstOrDefault().ClientNumber)

@{ ClientDetail dummyModel = null; }
@Html.DisplayNameFor(dummyParam => dummyModel.ClientNumber)

Further Explanation

If we want to see some of the fancy footwork involved in passing an expression, just look at the source code on DisplayNameFor or custom implementations like DescriptionFor. Here's an simplified example of what happens when we call DisplayNameFor with the following impossible expression:

 @Html.DisplayNameFor3(model => model.Details[-5].ClientNumber)

Dissecting the Expression Tree

Notice how we go from model.Details.get_Item(-5).ClientNumber in the lambda expression, to being able to identify just the member (ClientNumber) without executing the expression. From there, we just use reflection to find the DisplayAttribute and get its properties, in this case Name.

Upvotes: 6

Chris Pratt
Chris Pratt

Reputation: 239290

Sorry, your question is a little hard to understand, but I think the gist is that you want to get the display names for your properties, to use as headers, without requiring or first having to pick a particular item out of the list.

There's already built-in support for this. You simply just use the model itself:

@Html.DisplayNameFor(m => m.ClientNumber)

In other words, just don't use a particular instance. DisplayNameFor has logic to inspect the class the list is based on to get the properties.

Upvotes: 1

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