package Node;
use base 'My::Class::DBI';

... # standard Class::DBI stuff here

# Declare that we have a relationships table that
# tells us where our children are
Node->has_many('children_refs' => 'Relationship' => 'parent_id');

# Now that we can fetch those records from the
# relationships table, we need to have a way to
# get Node objects from those relationships
sub children {
  return Node->search_in(
    Node->primary_column => [
      map { $_->child_id } shift->children_refs
    ]
  );
}

# Similarly for parents