One thing I've done in one project using Class::DBI is to return a closure-as-an-iterator in scalar context (and void context, just because I'm lazy):

use My::DBI::Table;  # A Class::DBI instance
my $table; # Intitilized elsewhere

sub get_foos 
{
    my $foos = $table->foos();
    if(wantarray) {
        my @array;
        while(my $foo = $foos->next()) {
            push @array, $foo;
        }
        return @array;
    }
    else {
        return sub {
            my $foo = $foos->next() or return;
            return $foo;
        };
    }
}
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In the real project, the objects returned are actually passed into the constructor of a class that acts as a middle layer between the UI and the database, so the real method is slightly more complex than the above. As is, the above is just a thin layer over the regular Class::DBI methods (which already returns iterators on has_many relationships).