Filters and their order — ASP.NET Core MVC (and Razor Pages)

11. Filters and their order

Intermediate★ Must knowLesson 11 of 15

Filter	Runs	Example
Authorization	First; can short-circuit	`[Authorize]`, custom policy checks
Resource	Before/after model binding	Caching, short-circuit for maintenance
Action	Before/after the action method	Logging, validation, modifying arguments
Exception	When an unhandled exception occurs in the MVC pipeline	Convert to error view/ProblemDetails
Result	Before/after the result executes	Add headers, modify the result

csharp

public class AuditFilter(ILogger<AuditFilter> log) : IAsyncActionFilter
{
    public async Task OnActionExecutionAsync(ActionExecutingContext ctx, ActionExecutionDelegate next)
    {
        log.LogInformation("Executing {Action}", ctx.ActionDescriptor.DisplayName);
        var executed = await next();
        if (executed.Exception is null) log.LogInformation("Done {Action}", ctx.ActionDescriptor.DisplayName);
    }
}
builder.Services.AddControllersWithViews(o => o.Filters.Add<AuditFilter>());   // global
// or [ServiceFilter(typeof(AuditFilter))] on a controller/action (filter resolved from DI)

Scope order: global → controller → action on the way in (reverse on the way out); override with Order.

Filters vs middleware: middleware sees every request (including static files) and knows nothing about MVC; filters run only for MVC actions and have access to ModelState, action arguments and results.