In Class::DBI we declare these table relationships in our Class:
package FilmBuff::DBI;
use base 'Class::DBI';
FilmBuff::DBI->set_db('Main', 'dbi:mysql:database=test', 'test', '');
# FilmBuff::Person
package FilmBuff::Person;
use base 'FilmBuff::DBI';
FilmBuff::Person->table('person');
FilmBuff::Person->columns('id', 'name');
FilmBuff::Person->columns(Primary => 'id');
FilmBuff::Person->has_many('credits', FilmBuff::Credit => 'person_id');
# FilmBuff::Film
package FilmBuff::Film;
use base 'FilmBuff::DBI';
FilmBuff::Film->table('film');
FilmBuff::Film->columns('id', 'title', 'year');
FilmBuff::Film->columns(Primary => 'id');
FilmBuff::Film->has_many('credits', FilmBuff::Credit => 'film_id');