ASP.NET Core MVC Interview Question #97

What is the difference between synchronous and asynchronous MVC filters?

Advanced Routing, Filters, Areas & Application Structure Mid-Level Intermediate

Quick Interview Answer

MVC provides synchronous filter interfaces such as IActionFilter and asynchronous equivalents such as IAsyncActionFilter. An asynchronous filter should be used when its work requires asynchronous I/O.

Detailed Explanation

Async filters call and await the provided continuation delegate to execute the next stage. Avoid blocking asynchronous operations with .Result or .Wait() inside filters.

Code Example

public sealed class AuditFilter : IAsyncActionFilter
{
    public async Task OnActionExecutionAsync(
        ActionExecutingContext context,
        ActionExecutionDelegate next)
    {
        await WriteAuditStartAsync();
        var executed = await next();
        await WriteAuditEndAsync(executed);
    }
}