Function backend_db 

pub async fn backend_db<'c, DB, C, C1>(
    c: C,
) -> Result<(DBType, AdapterExecutor<'c, DB, C>), Error>
where
    DB: Database,
    C: Executor<'c, Database = DB> + 'c + Deref<Target = C1>,
    C1: Any + 'static,