ActionFilterAttribute: When to use OnActionExecuting vs. OnActionExecutingAsync?

Difference between OnActionExecting and OnActionExecutingAsync

Both are ActionFilters can be added as attributes on Controller methods. OnActionExecting and OnActionExecutingAsync are both called before the controller action method is executed.

The difference is OnActionExecuting runs SYNCHRONOUSLY and OnActionExecutingAsync should be used when you want to run some ASYNCHRONOUS calls.

OnActionExecuting Implementation

public class ActionFilter : Attribute, IActionFilter
    {
        private ILoggerEntry _loggerEntry;
        public ActionFilter(ILoggerEntry loggerEntry)
        {
            _loggerEntry = loggerEntry ?? throw new ArgumentNullException("ILogger cannot be null");
        }

        public void OnActionExecuted(ActionExecutedContext actionContext)
        {
            _loggerEntry.AddToLog("Called after action method executes");
        }

        public void OnActionExecuting(ActionExecutingContext actionContext)
        {
            _loggerEntry.AddToLog("Called before action method executes. Executed Synchronously");
        }
    }

OnActionExecutingAsync Implementation

Use this when you want to add await statements to call asynchronous methods.

public class ActionFilterAsync : Attribute, IAsyncActionFilter
    {
        private ILoggerEntry _loggerEntry;

        public ActionFilterAsync(ILoggerEntry loggerEntry)
        {
            _loggerEntry = loggerEntry ?? throw new ArgumentNullException("ILogger cannot be null");
        }

        public async Task OnActionExecutionAsync(ActionExecutingContext actionContext, ActionExecutionDelegate next)
        {
             _loggerEntry.AddToLog("Called before action method executes. Executed Asynchronously");
            await _loggerEntry.LogErrorEntry();

            await next();
        }
    }

Now, you can invoke the attribute on a controller or any controller action method.

[ApiController]
[Route("[controller]")]
[ServiceFilter(typeof(ActionFilter))]
public class WeatherForecastController : ControllerBase