public function setPrimaryKey(array $columnNames, $indexName = false)
    {
        $this->_addIndex($this->_createIndex($columnNames, $indexName ?: 'primary', true, true));

        foreach ($columnNames as $columnName) {
            $column = $this->getColumn($columnName);
            $column->setNotnull(true);
        }

        return $this;
    }