How to use streams with MySql (works for postgres)

[mpiorowski]

So i had an sql query, one as vec, one as stream. The vectors one works great, the stream don't, but the excatly same functions works when i change it to postgres (don't mind the linting errors in the methods, my lsp broke ;p)

pub async fn get_notes_by_user_uuid(
    mut conn: Object<AsyncMysqlConnection>,
    user_uuid: Vec<u8>,
) -> Result<Vec<DieselNote>, Status> {
    let note = notes
        .select(DieselNote::as_select())
        .filter(user_id.eq(user_uuid))
        .filter(deleted.is_null())
        .load(&mut conn)
        .await
        .map_err(|e| Status::internal(e.to_string()))?;
    Ok(note)
}

pub async fn get_notes_by_user_uuid_stream_stream(
    mut conn: Object<AsyncMysqlConnection>,
    user_uuid: Vec<u8>,
) -> Result<impl Stream<Item = QueryResult<DieselNote>>, Status> {
    let note = notes
        .select(DieselNote::as_select())
        .filter(user_id.eq(user_uuid))
        .filter(deleted.is_null())
        .load_stream(&mut conn)
        .await
        .map_err(|e| Status::internal(e.to_string()))?;
    Ok(note)
}

[weiznich]

The issue here is that both stream types are not supposed to be equal. The postgres stream type is independent from the underlying connection, while the mysql stream type requires a connection for the whole time. That means the connection must outlive the stream. That's not the case in your example, as the connection is dropped by the end of the get_notes_by_user_uuid_stream_stream function, while the stream itself is returned by that function.