How to migrate from diesel to diesel_async with Rust-code migrations

[Ploppz]

We are migrating from diesel to diesel_async and we have some DB migrations written in Rust, which goes like

pub fn run(conn: &mut dyn BoxableConnection<Pg>) -> MResult<()> {
    let conn = conn.downcast_mut::<PooledConnection<ConnectionManager<PgConnection>>>().unwrap();

I tried to downcast to Object<AsyncPgConnection> instead (from diesel_async) but it said that it doesn't satisfy diesel::Connection trait. I guess instead it satisfies diesel_async::AsyncConnection trait.

Now, perhaps I could have kept the code the same but I removed "r2d2" feature from diesel dep because in no other part of the code than here is it required. And besides, I don't know if I could expect that to work because I now use async connection pool anyway. So it's not clear how such a migration is supposed to be migrated in diesel_async

[weiznich]

You need to provide the exact same connection type there that is used to run the migrations on. It's hard to say which type that is as you did not share that part of your code.

[Ploppz]

edit: short version: I can't find a way to provide async connection to the migration process.

---

It's a bit complicated right now because in the process of migrating the whole codebase, starting at the errors I'm facing now I haven't been able to update the migration code exactly to diesel-async.
However, looking at it now, diesel_migration::MigrationHarness::run_pending_migrations requires a diesel::connection::Connection. And this is a corner issue in general in the diesel-async-migration process for me, because it turns out that Object<AsyncPgConnection> (the connection that is returned from the async pool) does not implement Connection.

So do I have to understand it this way:
We have to keep r2d2 feature of diesel and use the regular blocking connection that we used before migrating, only for the purpose of running the migrations?

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edit:
This is how we run the migrations:

            let mut conn = s.get_conn().await.context("Connect to database")?;
            conn.run_pending_migrations(AllMigrations)?;

And AllMigrations is a struct that impl MigrationSource<Pg> and its migrations function returns a mix of all the SQL migrations and the Rust-code migrations.

[weiznich]

Maybe you have a look at the relevant example? That is linked several times from previous discussions. As written before: If you want to receive a specific type from a BoxableConnection it needs to be exactly that type you put in before.

[Ploppz]

Sorry, that is indeed a very relevant example, I should have looked in examples.