package Obj;

my %bar_cache;

sub new {
    my ($class, %args) = @_;
    my $dbh = $args{dbh}
    my $cfg = $args{cfg};
    my $obj_id = $args{obj_id};
  
    my $in = {
        dbh => $dbh,
        cfg => $cfg,
        foo => {},
        bar => {},
    };
    
    my $self = bless $in, $class;
    
    # foo is a result of a different query for every obj_id
    $in->{foo} = $self->foo($obj_id);

    # The following part is the only part I am still confused about.
    # Should I use something like Memoize here?
    #
    # bar changes only once per, say, every 5000 objects,
    # and the resulting query from $self->bar is a very 
    # large set (thousands of rows), so it makes sense to 
    # query the db only when bar changes. So, for obj_id 
    # 0 through 4999, bar remains the same, then for obj_id
    # 5000 through 9999 a new bar is returned, and so on
    $in->{bar} = $self->bar($obj_id);
    
    return $self;
}

sub bar {
    my ($class, $obj_id) = shift;

    if ($self->{bar}) {
        return $self->{bar};
    }
    else {
        if (exists $bar_cache{$obj_id}) {
            $self->{bar} = $bar_cache{$obj_id};
        }
        else {
            my $dbh = $self->dbh;
            my $bar = query_dbh_for_bar_execute($obj_id);
            
            # Empty bar_cache of old values
            %bar_cache = ();
            $bar_cache{$obj_id} = $bar;
            $self->{bar} = $bar_cache{$obj_id};
        }

        return $bar;    
    }

}