How do you seed data in migrations using ActiveModels?

[billy1624]

Discussed in #519

^{Originally posted by Drakota February 13, 2022}
I'm trying to seed data directly inside a migration, but I'm unable to get a DatabaseConnection handle to be able to do it.

let db = manager.get_connection();

let board = board::ActiveModel {
    name: Set("Test Board".to_owned()),
    ..Default::default()
};

board.save(db).await?;

I tried something like this, but I'm getting:
the size for values of type 'dyn sea_schema::migration::sea_orm::ConnectionTrait' cannot be known at compilation time the trait 'std::marker::Sized' is not implemented for 'dyn sea_schema::migration::sea_orm::ConnectionTrait'.