How to enable the effect of "using" for a view?

The page I'm developing's had the syntax as follows.

@model List<Group>
@{ Layout = "~/Views/Shared/_Layout.cshtml"; }

All of the sudden, because of a change that I'm not aware of (and can't retrace), VS starts demanding that I specify a full qualifier like this.

@model System.Collections.Generic.List<Group>
@{ Layout = "~/Views/Shared/_Layout.cshtml"; }

When I do that, Resharper marks it as necessary (which it should be, according to the code from before). My guess is that I've unknowingly removed a using somewhere but I can't figure of where.

Since I'm using Razor and MVC, there's no code-behind and frankly speaking I wonder where the information about that the List came from before it broke. I mean, there's got to be an information about the full qualifier System.Collections.Generic somewhere. Where is it supposed to be?

Solution

The framework will use namespaces defined in the Web.config found in the Views folder (not the application Web.config). The syntax looks like:

<system.web.webPages.razor>
  <pages pageBaseType="System.Web.Mvc.WebViewPage">
    <namespaces>
      <add namespace="System.Collections.Generic" />
    </namespaces>
  </pages>
</system.web.webPages.razor>

You can also use a namespace in a single file using the syntax:

using System.Collections.Generic