.NET 7 minimal API AsParametersAttribute not mapping my request model as expected

Question

I am trying to implement a simple generic minimal API MediatR method mapper (inspired by this video). I ran into an issue regarding mapping my request model when receiving data from body in the POST method with AsParametersAttribute.

I've double checked in documentation that this is possible, but...

• Using AsParametersAttribute I don't get any data in the model
• Using FromBodyAttribute I get the data in the model as expected.
• SignInRequest is a simple model which I've tried to convert to everything - class, record struct. It doesn't work with [AsParameters]. The IHttpRequest is just simplification of MediatR's IResult<TResponse> with my custom response model.

Answer 1

AsParametersAttribute is used to group handler parameters into a single data structure:

Specifies that a route handler delegate's parameter represents a structured parameter list.

I.e. if you have the following endpoint:

app.MapPost("sign-in", async (IMediator mediator, SignInRequest request) => ...);

This attribute will allow you to introduce a data structure to encapsulate those parameters:

public struct SignInHandlerParams
{
   public IMediator Mediator {get; set;}

   public SignInRequest Request {get; set;}
}

app.MapPost("sign-in", async ([AsParameters]SignInHandlerParams p ) => ...);

It does not replace the FromBody, FromServices etc. in any way.

Check out the parameter binding for argument lists with AsParameters doc for more details.