code: protected function getJoin()
      {
          if (!empty($this->joins)) {
              $joins = array();
              foreach ($this->joins as $join) {
                  $manager = $join['manager'];
                  $st = array();
  
                  if ($join['type']) {
                      $st[] = $join['type'];
                  }
  
                  if ($join['column']) {
                      $column = $join['column'];
                  } else {
                      $column = $this->pk;
                  }
  
                  if ($join['column_right']) {
                      $column_right = $join['column_right'];
                  } else {
                      $column_right = $manager->pk;
                  }
  
                  $st[] = "JOIN `" . $manager->table . "`";
  
                  $st[] = "ON (";
                  $st[] = "`" . $this->table . "`.`" . $column . "`";
                  $st[] = "=";
                  $st[] = "`" . $manager->table . "`.`" . $column_right . "`";
                  $st[] = ")";
                  $joins[] = implode(' ', $st);
                  $joins[] = $manager->getJoin();
              }
              return implode("\n", $joins);
          }
          return null;
      }
docs: Get Join