How to dispose objects correctly (ASP.NET MVC   Entity Framework)
public ActionResult Detail(Guid id)
{
    Attachment attachment = null;
    using (var attachmentRepository = IoC.Resolve<AttachmentRepository>())
    {
        attachment = attachmentRepository.SelectByKey(id);
        return View("Detail", attachment);
    }
}

public ActionResult Detail(Guid id)
{
    Attachment attachment = null;
    var attachmentRepository = IoC.Resolve<AttachmentRepository>();

    attachment = attachmentRepository.SelectByKey(id);
    return View("Detail", attachment);
}