我需要在生产环境中为基于 Rocket 的应用运行 Diesel 数据库迁移。通常有以下几种方法可以对数据库执行迁移:
- 在应用程序启动时。
- 与应用程序启动分开。
我更喜欢通过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就如何进行迁移提出建议:
- Add
diesel_migrations
to your dependencies- Include an
extern crate diesel_migrations
in your crate, and make sure to decorate it with#[macro_use]
- At the beginning of your code, add
embed_migrations!()
- To run the migrations, Use
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?
最佳答案
在谷歌上搜索了更多并找到了工作示例 here .
关键代码
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())
}
关于database - 如何在生产环境中使用 Rocket 运行 Diesel 迁移?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/61047355/