Best way to do global viewdata in an area of my ASP.NET MVC site?

Question

I have an several controllers where I want every ActionResult to return the same viewdata. In this case, I know I will always need basic product and employee information.

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Answer 1

You could write a custom action filter attribute which will fetch this data and store it in the view model on each action/controller decorated with this attribute.

public class GlobalDataInjectorAttribute : ActionFilterAttribute
{
    public override void OnActionExecuted(ActionExecutedContext filterContext)
    {
        string id = filterContext.HttpContext.Request["id"];
        // TODO: use the id and fetch data
        filterContext.Controller.ViewData["employeeName"] = employeeName;
        filterContext.Controller.ViewData["productName"] = productName;
        base.OnActionExecuted(filterContext);
    }
}

Of course it would much cleaner to use a base view model and strongly typed views:

public class GlobalDataInjectorAttribute : ActionFilterAttribute
{
    public override void OnActionExecuted(ActionExecutedContext filterContext)
    {
        string id = filterContext.HttpContext.Request["id"];
        // TODO: use the id and fetch data
        var model = filterContext.Controller.ViewData.Model as BaseViewModel;
        if (model != null)
        {
            model.EmployeeName = employeeName;
            model.ProductName = productName;
        }
        base.OnActionExecuted(filterContext);
    }
}

Now all that's left is to is to decorate your base controller with this attribute:

[GlobalDataInjector]
public abstract class BaseController: Controller
{ }

---

There's another more interesting solution which I personally prefer and which involves child actions. Here you define a controller which handles the retrieval of this information:

public class GlobalDataController: Index
{
    private readonly IEmployeesRepository _employeesRepository;
    private readonly IProductsRepository _productsRepository;
    public GlobalDataController(
        IEmployeesRepository employeesRepository,
        IProductsRepository productsRepository
    )
    {
        // usual constructor DI stuff
        _employeesRepository = employeesRepository;
        _productsRepository = productsRepository;
    }

    [ChildActionOnly]
    public ActionResult Index(int id)
    {
        var model = new MyViewModel
        {
            EmployeeName = _employeesRepository.Find(Thread.CurrentPrincipal.Identity.Name).First().FullName,
            ProductName = _productsRepository.Find(id).First().Name;
        };
        return View(model);
    }
}

And now all that's left is to include this wherever needed (probably the master page if global):

<%= Html.Action("Index", "GlobalData", new { id = Request["id"] }) %>

or if the id is part of the routes:

<%= Html.Action("Index", "GlobalData", 
    new { id = ViewContext.RouteData.GetRequiredString("id") }) %>