Convert web::Json<T> to &mut T

Question

I am trying to write a simple api to create user in actix-web but I need to pass the User object as mutable reference in the method db_connector.create_user() because it needs to be edited behind the scenes - in order to add id, creation-date etc.

#[post("/users")]
pub async fn create_user(
    db_connector: web::Data<DBConnector>,
    user: web::Json<User>,
) -> impl Responder {
    match db_connector.create_user(&user.into_inner()).await {
        Ok(_) => HttpResponse::Created().finish(),
        Err(e) => HttpResponse::InternalServerError().body(e.to_string()),
    }
}

But I am not sure how to convert web::Json<User> to &mut User. Thanks in advance for the help.

Answer 1

#[post("/users")]
pub async fn create_user(
    db_connector: web::Data<DBConnector>,
    web::Json(mut user): web::Json<User>,
) -> impl Responder {
    match db_connector.create_user(&mut user).await {
        Ok(_) => HttpResponse::Created().finish(),
        Err(e) => HttpResponse::InternalServerError().body(e.to_string()),
    }
}

should work fine, though I didn't test it (and don't know actix).

According to the documentation Json is

pub struct Json<T>(pub T)

so it's a trivial wrapper you can pattern match on, and you just need to have a mutable binding in order to create a mutable reference from it.

Alternatively if you want to keep the existing binding style for some reason,

#[post("/users")]
pub async fn create_user(
    db_connector: web::Data<DBConnector>,
    mut user: web::Json<User>,
) -> impl Responder {
    match db_connector.create_user(&mut user.0).await {
        Ok(_) => HttpResponse::Created().finish(),
        Err(e) => HttpResponse::InternalServerError().body(e.to_string()),
    }
}

same deal, just without the pattern-based deconstruction of the input Json.

Hell, even just

#[post("/users")]
pub async fn create_user(
    db_connector: web::Data<DBConnector>,
    user: web::Json<User>,
) -> impl Responder {
    match db_connector.create_user(&mut user.into_inner()).await {
        Ok(_) => HttpResponse::Created().finish(),
        Err(e) => HttpResponse::InternalServerError().body(e.to_string()),
    }
}

probably works.