如何在生产中使用 Rocket 运行 Diesel 迁移？

Question

我需要在生产环境中为基于 Rocket 的应用程序运行 Diesel 数据库迁移。通常有几种方法可以为数据库执行迁移：

1. 在应用程序启动时。
2. 独立于应用程序启动。

我更喜欢使用应用程序二进制文件的--migrate 标志调用的第二个选项，但由于目标应用程序相当简单，第一种方法就可以了。

有一个 thread in the Diesel issue tracker 关于在生产中运行迁移并建议如何进行：

1. 将diesel_migrations 添加到您的依赖项中
2. 在您的箱子中添加一个extern crate diesel_migrations，并确保用#[macro_use] 装饰它
3. 在代码的开头添加embed_migrations!()
4. 要运行迁移，请使用 embedded_migrations::run(&db_conn)

在main.rs我做了：

#![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
    ...
}

这会导致错误：

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)

如何解决？

Answer 1

谷歌了一些，找到了工作示例here。

键码

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())
}

Answer 2

以 SS_Rebelious 的回答为基础，这就是我必须为 Rocket 0.5 做的事情

#[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
}