I Cannot find the way to do that
I need 3 group of artists for albums and the possibility to choose more than one in each group

Is there any possibility to modify your code for more flexibility ?
your table #__muscol_artists
+ a table #__muscol_artist_category (with author, artist, musicians , whatever ..)
+ a cross table #__muscol_artists_albums to associate an album to as many artists as needed

Hello Erick,

Unfortunately there's only one field for artist (and it has no "group" associated).
The way to go would be to create tables such as the one you mention, but this is very very big thing to do. You would basically need to change avery single file within music collection to work that way.

To create a table #__muscol_artists_albums is something we are already planning for a future release, so that will be included eventually. However there are no plans for the "category" assignation (what you would use in your case because you are using it as a movie databasae, I understand, and you need director, author, etc..)

Then I have lost 75 € and a good week of work ... I cannot use you extension

You have not lost anything, if you don't want to use our extension we can refund your purchase without problem Erick...

How much will you charge to do that job now ? to assign multi artists to an album ? with cross table
how much and how long

You've got an email for that custom code
we can also speak on Skype maybe ?