code: public function up()
      {
          $cache = $this->getCache();
          $this->db = $cache->db;
  
          $tableOptions = null;
          if ($this->db->driverName === 'mysql') {
              // http://stackoverflow.com/questions/766809/whats-the-difference-between-utf8-general-ci-and-utf8-unicode-ci
              $tableOptions = 'CHARACTER SET utf8 COLLATE utf8_unicode_ci ENGINE=InnoDB';
          }
  
          $this->createTable($cache->cacheTable, [
              'id' => $this->string(128)->notNull(),
              'expire' => $this->integer(),
              'data' => $this->binary(),
              'PRIMARY KEY ([[id]])',
              ], $tableOptions);
      }
docs: {@inheritdoc}