Monday, October 11, 2021

ASP.NET Core–Route arguments are case sensitive

I’m currently rewriting an existing ASP.NET Web API application to ASP.NET Core. Along the way I encountered some issues, here is one specific lesson I learned…

After porting an ASP.NET Web API controller to .NET Core, a specific action method looked like this:

Looked OK to me. But when I tried to invoke this action method, I got a 400 error back:

  "type": "",
  "title": "One or more validation errors occurred.",
  "status": 400,
  "traceId": "00-3c02d7d0541cbb49a1790b11a71d871a-885c9350d2c4864c-00",
  "errors": {
    "ID": [
      "The value '{id}' is not valid."
It wasn’t immediatelly obvious to me what I did wrong. Maybe you spot my mistake?
Let’s have a look at the route attribute: [HttpGet(“{id}”)]
and at the method argument: GetAuthTypeById(int ID)
As you can see the ‘id’ argument in the route is lowercase where the method argument is uppercase. Turns out that this is the cause of the error above.
To make it work, I have to make sure that both the route attribute and method argument are using the exact same casing: