Wednesday, October 6, 2021

ASP.NET Core - How to handle the ‘NotFound’ use case when using a typed controller

I’m currently rewriting an existing ASP.NET Web API application to ASP.NET Core. While doing that, I (re)discovered some ASP.NET Core features I forgot they existed.

One of the features that ASP.NET Core offers are ‘typed controllers’. I don’t think that is the official name but you’ll know what I mean when you take a look at the example below:

In the example above I created an action method GetTodoItem that returned a typed object of type ‘TodoItem’ (or to be even more correct a Task<TodoItem>).  This makes your life as a developer easy as you don’t have to think about the ins and outs of ASP.NET. It almost feels like that this action method is exactly the same as any other method you’ll find on a class.

But what if wanted to return a 404 message when no TodoItem could be found for the specified id. Should I throw a specific exception? In ASP.NET Web API this was possible through the use of the HttpResponseException.

In ASP.NET Core there is a better alternative through the usage of ActionResult<T>. By wrapping the returned object in an ActionResult I can keep most of my code(thanks to the magic of implicit cast operators) and start using ActionResult types for specific use cases.

Let’s rewrite our example: