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I'm trying to make dynamic menu (stored in DB), that is showing on all web app pages. Using Google I found that it is better to make menu view as a part of Master View (_Layout.cshtml). And because of that, every action method of the controller must contain data with the menu model. To avoid code duplication I found the solution to create a base controller and provide data using its constructor:

https://learn.microsoft.com/en-us/aspnet/mvc/overview/older-versions-1/views/passing-data-to-view-master-pages-cs

Also, I'm trying to use async/await possibilities and my PageService (menu) is using ToListAsync() to get data from DB. So now I have a problem, that BaseController constructor has an async method:

public class BaseController : AsyncController, IBaseController
{
    private readonly IPageService _pageService;

    public BaseController(IPageService pageService)
    {
        _pageService = pageService;
        SetBaseViewModelAsync();
    }

    private async Task SetBaseViewModelAsync()
    {
        ViewData["Pages"] = await _pageService.GetAllAsync();
    }
}

I know that this is BAD CODE, but I don't know how to design this situation properly. Maybe there is another better way to create the dynamic menu or another way to get data asynchronously?

Also, I found this article, but I don't know if I can apply its solutions because I don't know if I can handle controller instance creation:

http://blog.stephencleary.com/2013/01/async-oop-2-constructors.html

Dima Glushko
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  • That's bad design, you are correct there. You should be looking at a middle-ware or action filter instead – Camilo Terevinto Dec 22 '17 at 17:29
  • Thanks for the response! Can you please provide some links to articles with proper designs? Because I googled for like 1-2 hours to find how to implement the dynamic menu. – Dima Glushko Dec 22 '17 at 17:33
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    This sounds like a good candidate for a [Child Action](https://stackoverflow.com/questions/12530016/what-is-an-mvc-child-action). See also this question https://stackoverflow.com/questions/21948909/asp-net-mvc-controller-for-layout – Jasen Dec 22 '17 at 17:38
  • @Jasen, RenderAction can't call async Actions – Dima Glushko Dec 24 '17 at 20:52

2 Answers2

6

Instead of deriving everything from a base controller (which can be a lot of extra work and testing) you can just create a controller called MenuController, create a method called Default and then call it from your Layout:

[ChildActionOnly]
public Default()
{
  var viewModel = _pageService.GetAllAsync();
  return Partial(viewModel);
}

in your layout:

@{Html.RenderAction("Default", "Menu");}

This is really the easiest and cleanest solution. The biggest PRO is that you can control the cache for the menu separate from the method calling. There are no good solution for asp.net-mvc (1-5) to run Async code in this fashion. (ActionFilters can't be async and (Render)Partials can't be async. You can still call an async method, it will just run Sync.

Render vs Non-Render Performance.

Erik Philips
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  • Thanks for the response! I am new to MVC, so I will read about RenderAction and will try your solution. Also, cache possibility is great here! – Dima Glushko Dec 22 '17 at 17:45
  • Applied your solution, but it has some nuances: child actions can't be async: https://stackoverflow.com/questions/24072720/async-partialview-causes-httpserverutility-execute-blocked-exception/47962963#47962963 So I decided not to make the action as ChildAction. Is it necessary to make it child only? Can you please also modify your answer, so acceptance would be proper? Because now your example has async code in ChildAction – Dima Glushko Dec 24 '17 at 18:04
  • Async code has async/await keywords. Mine does not use those keywords. It should compile with a warning. Otherwise you could just [call async code within a sync method](https://stackoverflow.com/questions/9343594/how-to-call-asynchronous-method-from-synchronous-method-in-c/25097498#25097498). – Erik Philips Dec 24 '17 at 18:19
  • Calling async code within sync method is a bad idea. IMO I will better remove ChildAction attribute and remain code async – Dima Glushko Dec 24 '17 at 19:10
  • I was wrong, that was just my cache, that returned the correct result to me. I removed the cache and I'm getting the same as here error: https://stackoverflow.com/questions/24072720/async-partialview-causes-httpserverutility-execute-blocked-exception/47962963#47962963 So I can't use RenderAction with async Actions... Then I will just call sync method. Seems like it's impossible to realize my problem with the async code. – Dima Glushko Dec 24 '17 at 20:51
-1

I changed functionality to call Html.RenderAction in my View, as Erik Philips suggested:

@{
    Html.RenderAction("Index", "Pages");
}

and controller:

public class PagesController : AsyncController, IPagesController
{
    private readonly IPagesService _pagesService;

    public PagesController(IPagesService pagesService)
    {
        _pagesService = pagesService;
    }

    [HttpGet]
    [Route("")]
    public async Task<ActionResult> IndexAsync()
    {
        var viewModel = await _pagesService.GetAllAsync();
        return PartialView("MenuPartial", viewModel);
    }
}

But RenderAction doesn't work with async controller Actions:

Async PartialView causes "HttpServerUtility.Execute blocked..." exception

So seems like sync call is the only one possible here.

Dima Glushko
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