public function getConstraintString() { $sql[] = parent::getConstraintString(); foreach ($this->references as $rk) { $reference_keys[] = $rk->getName(); } $reference_table_name = $rk->getTable()->getFullName(); $sql[] = 'REFERENCES'; $sql[] = $reference_table_name . '(' . implode(', ', $reference_keys) . ')'; $sql[] = 'ON DELETE ' . $this->getOptionString($this->on_delete); $sql[] = 'ON UPDATE ' . $this->getOptionString($this->on_update); return implode(' ', $sql); }