How to share a transaction between repositories?

Question

I use sqlx to communicate with my Postgres database. I'm trying to abstract the database communication with a Repository pattern. Aslo, with this abstraction I would like to share the database transaction between repositories using Unit Of Work pattern. The only problem that I have I don't know how to share the sqlx transaction between those repositories without explicitly providing transaction in save arguments (e.g. repository_x.save(entity, transaction)). I would like to create and share transactions in uow (unit of work) abstraction.

I want to achieve something like this

struct CommandHandler {
  unit_of_work: UnitOfWork
}

impl CommandHandler {
  pub fn handle(&self, &command: Command) {
    let repository_a = self.unit_of_work.repository_a();
    let repository_b = self.unit_of_work.repository_b();    

    let entity_a = repository_a.get_by_id(command.id);
    let entity_b = repository_b.get_by_id(entity_a.id);


    unit_of_work.start_transaction();

    repository_a.save(entity_a);
    repository_b.save(entity_b);

    unit_of_work.commit_transaction();
  }
}

Does anyone know what the implementation of the unit_of_work struct would look like to execute the above example?