ASP.Net Core WebApi - storing values from ActionFilter to access in controller

Question

In an ASP.Net Core WebApp I want to use an ActionFilter and send information from the ActionFilter to the controller it is applied to.

MVC

For MVC I can do this

ActionFilter

    public class TenantActionFilter : IActionFilter
    {
        public void OnActionExecuting(ActionExecutingContext context)
        {
            //Using some sneaky logic to determine current tenant from domain, not important for this example
            int tenantId = 1;
            Controller controller = (Controller)context.Controller;
            controller.ViewData["TenantId"] = tenantId;
        }
        public void OnActionExecuted(ActionExecutedContext context) { }
    }

Controller

    public class TestController : Controller
    {
        [ServiceFilter(typeof(TenantActionFilter))]
        public IActionResult Index()
        {
            int tenantId = ViewData["TenantId"];
            return View(tenantId);
        }
    }

It works and I can pass data back to the controller via ViewData - great.

WebApi

I want to do the same for WebApi Controllers.

The actionFilter itself can be applied, runs etc - but I cannot write to ViewData, because WebAPI inherits from ControllerBase - not from Controller (like MVC).

Question

How can I push data from my ActionFilter back to the calling ControllerBase, similar to MVC?

Notes

ASP.Net Core 2.2 being used, but I would be surprised if a solution would not be usable in all of .Net Core.

Kjensen · Accepted Answer · 2020-02-05 16:35:32Z

5

...So I found the answer when I was almost done writing the question, so here goes...

The answer is the HttpContext.Items collection

ActionFilter

    public class TenantActionFilter : IActionFilter
    {
        public void OnActionExecuting(ActionExecutingContext context)
        {
            int tenantId = 1;
            var controller = (ControllerBase)context.Controller;
            controller.HttpContext.Items.Add("TenantId", tenantId);
        }
        public void OnActionExecuted(ActionExecutedContext context) { }
    }

Controller

    public class TestApiController : ControllerBase
    {
        [ServiceFilter(typeof(TenantActionFilter))]
        public SomeClass Get()
        {
            int tenantId;
            if (!int.TryParse(HttpContext.Items["TenantId"].ToString(), out tenantId))
            {
                tenantId = -1;
            }
            return new SomeClass();
        }
    }

answered Feb 5, 2020 at 16:35

Kjensen

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2 Comments

Robert Harvey Over a year ago

Holding state seems at odds with the notion of a stateless controller.

Kjensen Over a year ago

For a multitenant application, I need to determine which domain the method called is associated with. I could do that directly in the actionmethod, but wrapping it up in a reusable actionfilter seems much cleaner - to me at least.

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