Custom extractor to validate query string.

[goni098]

I custom extractor by implementing FromRequest to validate query struct and i get the error that "the trait FromRequest<(), Body, _> is not implemented for Validated". Here my implementation, some one help me please .

```
use axum::{async_trait, extract::{FromRequest,Query}, http};
use validator::Validate;

pub struct Validated<T>(pub T);

#[async_trait]
impl<S, B, T> FromRequest<S, B> for Validated<T>
where
  T: Validate,
  S: Send + Sync,
  B: Send + 'static,
  Query<T>: FromRequest<S, B>,
{
  type Rejection = (http::StatusCode, String);

  async fn from_request(req: http::Request<B>, state: &S) -> Result<Self, Self::Rejection> {
    let query = Query::<T>::from_request(req, state).await;

    if let Ok(Query(data)) = query {
      match data.validate() {
        Ok(_) => Ok(Validated(data)),
        Err(err) => Err((http::StatusCode::BAD_REQUEST, err.to_string())),
      }
    } else {
      Err((
        http::StatusCode::INTERNAL_SERVER_ERROR,
        "internal server error".to_string(),
      ))
    }
  }
}

// my handler
#[derive(Deserialize, Serialize, Validate)]
pub struct Pagination {
  #[validate(range(min = 1))]
  page: usize,

  #[validate(range(max = 100))]
  per_page: usize,
}


#[axum_macros::debug_handler]
pub async fn get_query_string(
  Validated(pagination): Validated<Pagination>,
) -> response::Json<Pagination> {
  response::Json(pagination)
}


```

[davidpdrsn]

The issue is actually with the Query<T>: FromRequest<S, B> bound. You'll wanna use Query<T>: FromRequestParts<S> instead since Query doesn't need the request body.

This works for me

use axum::{
    async_trait,
    extract::{FromRequest, FromRequestParts, Query},
    http, response,
};
use serde::{Deserialize, Serialize};
use validator::Validate;

pub struct Validated<T>(pub T);

#[async_trait]
impl<S, B, T> FromRequest<S, B> for Validated<T>
where
    S: Send + Sync,
    B: Send + 'static,
    T: Validate,
    Query<T>: FromRequestParts<S>,
{
    type Rejection = (http::StatusCode, String);

    async fn from_request(req: http::Request<B>, state: &S) -> Result<Self, Self::Rejection> {
        let query = Query::<T>::from_request(req, state).await;

        if let Ok(Query(data)) = query {
            match data.validate() {
                Ok(_) => Ok(Validated(data)),
                Err(err) => Err((http::StatusCode::BAD_REQUEST, err.to_string())),
            }
        } else {
            Err((
                http::StatusCode::INTERNAL_SERVER_ERROR,
                "internal server error".to_string(),
            ))
        }
    }
}

// my handler
#[derive(Deserialize, Serialize, Validate)]
pub struct Pagination {
    #[validate(range(min = 1))]
    page: usize,

    #[validate(range(max = 100))]
    per_page: usize,
}

#[axum::debug_handler]
pub async fn get_query_string(
    Validated(pagination): Validated<Pagination>,
) -> response::Json<Pagination> {
    response::Json(pagination)
}

[goni098]

thank you so much !