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home / developersection / interviews / what are filters in asp.net mvc/web api? types and use cases?
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What are filters in ASP.NET MVC/Web API? Types and use cases?

Ravi Vishwakarma 714 13 Jun 2025
c# c#
Updated 13 Jun 2025
Ravi Vishwakarma
Ravi Vishwakarma

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Ravi Vishwakarma is a dedicated Software Developer with a passion for crafting efficient and innovative solutions. With a keen eye for detail and years of experience, he excels in developing robust software systems that meet client needs. His expertise spans across multiple programming languages and technologies, making him a valuable asset in any software development project.

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Ravi Vishwakarma
Ravi Vishwakarma 13 Jun 2025
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In ASP.NET MVC and ASP.NET Web API, filters are used to execute custom logic before or after specific stages in the request processing pipeline — such as authentication, authorization, model binding, or action execution.

What Are Filters?

Filters are attributes (decorators) that allow code to run:

  • Before/After an action method executes
  • Before/After a result is returned
  • Globally, per-controller, or per-action

They enable cross-cutting concerns like:

  • Logging
  • Exception handling
  • Caching
  • Authorization
  • Performance monitoring

Types of Filters

Filter Type Interface / Base Class Runs When? Common Use Case
Authorization Filter IAuthorizationFilter (MVC) / AuthorizeAttribute Before controller/action is invoked User access control
Action Filter IActionFilter / ActionFilterAttribute Before & after action method executes Logging, audit
Result Filter IResultFilter / ResultFilterAttribute Before & after action result executes Modify view result
Exception Filter IExceptionFilter / ExceptionFilterAttribute On unhandled exceptions Global error handling
Resource Filter (MVC Core/Web API Core) IResourceFilter Around entire request lifecycle Caching, short-circuiting

Filter Execution Order

  • Authorization Filters
  • Resource Filters (ASP.NET Core)
  • Action Filters
  • Result Filters
  • Exception Filters (fires if exceptions occur)

Examples

1. Authorization Filter

[Authorize]
public class AdminController : Controller
{
    public ActionResult Dashboard() => View();
}

2. Custom Action Filter

public class LogActionFilter : ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext context)
    {
        // Log request data
    }

    public override void OnActionExecuted(ActionExecutedContext context)
    {
        // Log response or result
    }
}

Usage:

[LogActionFilter]
public ActionResult Index() => View();

3. Exception Filter

public class HandleExceptionFilter : FilterAttribute, IExceptionFilter
{
    public void OnException(ExceptionContext context)
    {
        // Log and handle
        context.ExceptionHandled = true;
        context.Result = new ViewResult { ViewName = "Error" };
    }
}

Filter Scopes

Filters can be applied at:

  • Global level (all controllers/actions)
  • Controller level
  • Action level
// Global
GlobalFilters.Filters.Add(new LogActionFilter());

// Controller
[LogActionFilter]
public class ProductController : Controller { ... }

// Action
[LogActionFilter]
public ActionResult Details(int id) { ... }

Use Cases Summary

Use Case Filter Type
Securing endpoints Authorization Filter
Logging user activity Action Filter
Modifying responses Result Filter
Handling global errors Exception Filter
Caching or short-circuit Resource Filter
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