Allow modifying the connection in migrations

[Lythenas]

New Features

Add a function to allow modifying the database connection in migrations.

This allows configuring the database connection like you do in your real application. I'm currently using this to register sqlite functions.

Usage would be something like this:

#[async_std::main]
async fn main() {
    cli::run_cli_with_connection(migration::Migrator, |connect_options| async {
        let db = Database::connect(connect_options)
             .await?;
        if db.get_database_backend() == DatabaseBackend::Sqlite {
            db::register_sqlite_functions(&db).await;
        }
        return Ok(db);
    }).await;
}

Note: I didn't see a test for run_cli except in the examples, so I wasn't sure if/where to add a test.

I also looked at adding it as a function to MigratorTrait but there we could at most accept a &DbConn (which would allow my use case) but I think this way is more flexible. The closure is accepting ConnectOptions so we can continue to use the same cli options and DATABASE_URL var. But it still allows to modify it before creating the connection or throw it away and create your own, if needed.

[tyt2y3]

thank you for your contribution. I think this is a nice idea, however can you make run_cli delegate to run_cli_with_connection ? I assume the following would work?

async fn run_cli(migrator: M) {
    run_cli_with_connection(migrator, Database::connect)
}

[Lythenas]

Yes thanks, I didn't think about that.