Hi Shadowsong, thanks very much for your reply and demo. I had seen that part of the doc and it looks promising, but the problem I am facing is that this filter ('N per "group"') must be applied after some other search calls on the RS.

Continuing the metaphor, this would be something like:

1. Restrict Artists to given musical genre
2. Restrict Albums to those release since given date
3. Restrict results to maximum N Albums per Artist

In my app I have the first two steps handled with methods in My::Schema::ResultSet::CD:

sub by_genre { $_[0]->search({ 'me.genre' => $_[1] });
sub since { $_[0]->search({ 'me.released' => { '>=', $_[1] } });
[download]

So the consuming code can do:

my $rs = $schema->resultset('CD');
if ( my $genre = param->{'genre'} ) {
    $rs = $rs->by_genre( $genre );
}
if ( my $since = param->{'since'} ) {
    $rs = $rs->since( $since );
}
[download]

I need to add a method that can act upon the existing ResultSet,

if ( my $limit = param->{'limit'} ) {
    $rs = $rs->limit_per_artist( $limit );
}
[download]

It's not clear to me that the doc you linked to and demoed can be adapted to search an existing RS, but I'll keep experimenting. Thanks again.