How to run Diesel migration with Rocket in production?

Question

I need to run Diesel database migrations in production for a Rocket-based app. Generally there are to ways to perform migrations for the database:

1. At application startup.
2. Separately from application startup.

I prefer the second option that would be invoked by using the --migrate flag for the application binary, but as the target application is fairly simple the first way will do just fine.

There is a thread in the Diesel issue tracker about running migrations in production and advise on how to do it:

1. Add diesel_migrations to your dependencies
2. Include an extern crate diesel_migrations in your crate, and make sure to decorate it with #[macro_use]
3. At the beginning of your code, add embed_migrations!()
4. To run the migrations, Use embedded_migrations::run(&db_conn)

In main.rs I made:

#![feature(proc_macro_hygiene, decl_macro)]

#[macro_use]
extern crate diesel;
#[macro_use]
extern crate diesel_migrations;

#[macro_use]
extern crate rocket;
#[macro_use]
extern crate rocket_contrib;

#[database("my_db_name")]
pub struct DbConn(diesel::PgConnection);

fn main() {
    // Update database
    embed_migrations!();
    embedded_migrations::run(&DbConn);
    // Launch the app
    ...
}

This leads to the error:

error[E0277]: the trait bound `fn(diesel::r2d2::PooledConnection<<diesel::PgConnection as rocket_contrib::databases::Poolable>::Manager>) -> DbConn {DbConn}: diesel::Connection` is not satisfied
  --> src/main.rs:30:30
   |
29 |     embed_migrations!();
   |     --------------------
   |     |
   |     required by this bound in `main::embedded_migrations::run`
30 |     embedded_migrations::run(&DbConn);
   |                              ^^^^^^^ the trait `diesel::Connection` is not implemented for `fn(diesel::r2d2::PooledConnection<<diesel::PgConnection as rocket_contrib::databases::Poolable>::Manager>) -> DbConn {DbConn}`
   |
   = note: required because of the requirements on the impl of `diesel_migrations::MigrationConnection` for `fn(diesel::r2d2::PooledConnection<<diesel::PgConnection as rocket_contrib::databases::Poolable>::Manager>) -> DbConn {DbConn}`
   = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

How to fix it?

Answer 1

Building off of SS_Rebelious' answer, here's what I had to do for Rocket 0.5

#[macro_use]
extern crate rocket;
#[macro_use]
extern crate diesel_migrations;

use capt_server::api::routes;
use diesel_migrations::embed_migrations;
use envy;
use rocket::fairing::AdHoc;
use rocket::{Build, Rocket};
use rocket_sync_db_pools::database;

#[database("sqlite_db")]
pub struct Db(diesel::SqliteConnection);

// This macro from `diesel_migrations` defines an `embedded_migrations` module
// containing a function named `run`. This allows the example to be run and
// tested without any outside setup of the database.
embed_migrations!();

#[launch]
fn rocket() -> _ {
    rocket::build()
        .attach(Db::fairing())
        .attach(AdHoc::try_on_ignite("Database Migrations", migrate))
        .mount("/", routes())
}

async fn migrate(rocket: Rocket<Build>) -> Result<Rocket<Build>, Rocket<Build>> {
    let db = Db::get_one(&rocket).await.expect("database connection");
    db.run(|conn| match embedded_migrations::run(&*conn) {
        Ok(()) => Ok(rocket),
        Err(e) => {
            error!("Failed to run database migrations: {:?}", e);
            Err(rocket)
        }
    })
    .await
}

Answer 2

Googled some more and found working example here.

Key code

use rocket::Rocket;
use rocket::fairing::AdHoc;

// This macro from `diesel_migrations` defines an `embedded_migrations` module
// containing a function named `run`. This allows the example to be run and
// tested without any outside setup of the database.
embed_migrations!();

#[database("sqlite_database")]
pub struct DbConn(SqliteConnection);

fn run_db_migrations(rocket: Rocket) -> Result<Rocket, Rocket> {
    let conn = DbConn::get_one(&rocket).expect("database connection");
    match embedded_migrations::run(&*conn) {
        Ok(()) => Ok(rocket),
        Err(e) => {
            error!("Failed to run database migrations: {:?}", e);
            Err(rocket)
        }
    }
}

fn rocket() -> Rocket {
    rocket::ignite()
        .attach(DbConn::fairing())
        .attach(AdHoc::on_attach("Database Migrations", run_db_migrations))
        .mount("/", StaticFiles::from("static/"))
        .mount("/", routes![index])
        .mount("/todo", routes![new, toggle, delete])
        .attach(Template::fairing())
}