pub async fn list_instances(pool: &State<sqlx::Pool<MySql>>, app_id: i64) -> Json<Vec<Instance>> {
    let instances = db::instance::list_instances(pool, app_id).await.unwrap();

pub async fn list_instances_by_region(
    pool: &State<sqlx::Pool<MySql>>,
    app_id: i64,
    region_id: i64,
    page: Option<i64>,
    per_page: Option<i64>,
) -> Json<Vec<Instance>> {
    // ... function body
}

pub async fn count_instances(pool: &State<sqlx::Pool<MySql>>) -> Json<i64> {
    let count = db::instance::count_instances(pool).await.unwrap();

pub async fn get_instance(pool: &State<sqlx::Pool<MySql>>, instance_id: i64) -> Json<Instance> {
    let instance = db::instance::get_instance_by_id(pool, instance_id)
        .await
        .unwrap();