Display tracks number next to Auto DJ and every playlist in Playlists and Crates, bug#991938

[weixindut]

The current implementation is by changing the name of each playlist and crate in the database, which is a straight forward way but with low efficiency and some constraints because of using some reg-exs. A better way is to add a name_displayed column in the table playlists and crates.

[kain88-de]

Hi

I just skimmed a bit over your code. I don't think we need a new sqltable column. Just make a second query for all the songs in the Playlist and check for it's size.

http://qt-project.org/doc/qt-4.8/qsqlquery.html#size

[weixindut]

Hi @kain88-de
The new sqltable column I used is used for caching the shown name, which can avoid using reg-ex with some constrains and finally improve the query performance. In fact, only at the last two commits 6d6a50d and ea83b95 I used the new column instead of a reg-ex to reimplement the function. You can have a look at the codes before the last two commits. I'm sorry I am not very clear about the meaning of just making a second query for all the songs and checking for it's size. How to avoid a new sqltable column through a second query?

[rryan]

I agree we should not change the database schema. Instead you can use a nested query and a join:

select Playlists.name, count_table.count from Playlists INNER JOIN 
  (select playlist_id, count(*) as count from PlaylistTracks 
  GROUP BY playlist_id) AS count_table 
  ON count_table.playlist_id = Playlists.id;

[weixindut]

Thanks @rryan. I am sorry for having ignored the performance of my sql statements. I will modify them later. And If both you and @kain88-de think it's better not to change the database schema, I will do a rollback.

[rryan]

@weixindut no worries! Also, the performance of your patch was fine. The nested query approach I posted is slightly slower when creating the list of playlist names but it eliminates the need to stick the track count in the title (and add getCrate/PlaylistByNameDisplayed which is a little awkward).

[kain88-de]

@weixindut do you still want to work on this?

[rryan]

Hi @weixindut -- I'm guessing you don't have time to work on this. Let us know if you want to finish it up at some point. Thanks!