code: public function join(
          BaseManager $manager,
          $type = null,
          $column = null,
          $column_right = null
      ) {
          $this->joins[$manager->table] = array(
              'manager' => $manager,
              'type' => $type,
              'column' => $column,
              'column_right' => $column_right
          );
          return $this;
      }
docs: Join managers together