How to run custom init code on a database connection?

[elibroftw]

Suppose I have a database ApiDatabase which is attached via .attach(ApiDatabase.init()).
What is the best or simplest manner to run code on rocket startup that utilizes this database connection?

[elibroftw]

use rocket::fairing::AdHoc;
use rocket::{Build, Rocket};

.attach(AdHoc::try_on_ignite("Create collection indexes", create_indexes))

pub async fn create_indexes(rocket: Rocket<Build>) -> fairing::Result {
    if let Some(db) = MainDatabase::fetch(&rocket) {

        return Ok(rocket);
    }
    Err(rocket)
}