Can I change my response data in OutputFormatter in ASP.NET Core 3.1 - asp.net-core

Question

I'm trying to create a simple feature to make the first action act like the second one.
public IActionResult GetMessage()
{
return "message";
}
public IActionResult GetMessageDataModel()
{
return new MessageDataModel("message");
}
First idea came to my mind was to extend SystemTextJsonOutputFormater, and wrap context.Object with my data model in WriteResponseBodyAsync, but the action is marked sealed.
Then I tried to override WriteAsync but context.Object doesn't have protected setter, either.
Is there anyway I can achieve this by manipulating OutputFormatter?
Or I have another option instead of a custom OutputFormatter?

Answer 1

for some reason they prefer every response in a same format like {"return":"some message I write.","code":1}, hence I want this feature to achieve this instead of creating MessageDataModel every time.
Based on your description and requirement, it seems that you'd like to generate unified-format data globally instead of achieving it in each action's code logic. To achieve it, you can try to implement it in action filter, like below.
public class MyCustomFilter : Attribute, IActionFilter
{
public void OnActionExecuted(ActionExecutedContext context)
{
// implement code logic here
// based on your actual scenario
// get original message
// generate new instance of MessageDataModel
//example:
var mes = context.Result as JsonResult;
var model = new MessageDataModel
{
Code = 1,
Return = mes.Value.ToString()
};
context.Result = new JsonResult(model);
}
Apply it on specific action(s)
[MyCustomFilter]
public IActionResult GetMessage()
{
return Json("message");
}