MVC Dropdown list from different entity

Question

I have a view, that is of Inherits from System.Web.Mvc.ViewPage<P>.

Type P has a property of Type C, ie, P could be:

class P
{
   public string Name { get; set; }
   public C OtherData { get; set; }
}

The View in question is for creating a new P, and as such I want to create a DropDown list of all the available C's.

So the dropdown could be:

C1
C2
C3
C4

I've tried creating the List<SelectListItem> object for the C's in my controller and then pass them to the view using ViewData but this does not work, as when I try to submit I get the exception:

System.InvalidOperationException: There is no ViewData item of type 'IEnumerable<SelectListItem>' that has the key C.

So my question is, how do I create a list of C objects to display in my View that inherits from type P. The list of objects is pulled from a database and as such I cannot just simply hardcode the options into the view.

Do I need to create another Model type that marries the 2 types together?

morganpdx · Accepted Answer · 2011-02-03 20:52:25Z

1

The way I do this is as follows:

ViewModel:

public class ViewModel
{
    public string Name { get; set; }
    public List<SelectListItem> ListOfCs { get; set; }
}

My View has the following:

<%:Html.EditorFor(model => model, new { ListOfCs = Model.ListOfCs })%>

I use the default Object.ascx outlined in Brad Wilson's excellent series of blog posts on ASP.NET MVC 2 Templates

Then I add a dropdown template for that dropdown in the Views/Shared/EditorTemplates folder and call it something like CClassDropDown:

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

<%: Html.DropDownList(null, new List<SelectListItem>(ViewData["ListOfCs"] as List<SelectListItem>), "Select C...")%>

And then I add a partial metadata class for the P object:

[MetadataType(typeof(PMetaData))]
public partial class P
{
    public class PMetaData
    {
        [UIHint("CClassDropDown")] 
        [DataType(DataType.Text)]
        public object C { get; set; }

    }
}

to the metadata for that class property so it knows to use the template I specified.

edited Feb 3, 2011 at 20:52

answered Feb 3, 2011 at 20:13

morganpdx

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5 Comments

AndrewC Over a year ago

Thanks morgan, Where do I add this metadata class? Never seen that before!

morganpdx Over a year ago

@AndyC - you would create a partial class for the containing object (P). You can find a great explanation of how to use it in the MVC Music Store tutorial: mvcmusicstore.codeplex.com. Look for "Using MetaData Partial Classes with Entity Framework". And incidentally, between that tutorial and Brad Wilson's templating series, I learned everything I need to know about MVC and EF4 (mostly!)

morganpdx Over a year ago

@AndyC as for where specifically to put the partial classes, I put them in the Model folder and I call them out with a .metadata.cs filename, so in this case: P.metadata.cs. Note that they are partial classes to the default EF4 generated classes - I don't usually do metadata partial classes on the viewmodel, although I did for your example.

AndrewC Over a year ago

@Morganpdx I assume this solution is still valid if I'm using Linq to Sql instead of EF? :)

morganpdx Over a year ago

@Andy - yes, it should work the same. The key point is the UIHint on the partial metadata class; that can be added to any class, not just an EF-generated one. You'll need to have the System.ComponentModel.DataAnnotations in your partial class for it to work.

Soraz · Accepted Answer · 2011-02-03 20:33:48Z

0

I've only done this with Linq2Sql so YMMW.

In Linq2Sql the entity has both an foreign entity, and a foreign entity key.

So, it would have both C and C_id.

class P
{
public string Name { get; set; }
public C OtherData { get; set; }
public int OtherData_id { get; set; }
}

In that case its just a case of doing

MyViewData {
  SelectList CList = new SelectList( ctx.getCs(), "C_id", "C_name")
}

and in the page doing

<%= Html.DropDownList("OtherData_id", Model.CList,"-") %>

In this way

TryModelUpdate(...)

will correctly set the OtherData_id, which in turn will cause OtherData to be resolved when accessed.

answered Feb 3, 2011 at 20:33

Soraz

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