code: public function cache($duration = null, $dependency = null)
      {
          $this->queryCacheDuration = $duration === null ? $this->db->queryCacheDuration : $duration;
          $this->queryCacheDependency = $dependency;
          return $this;
      }
docs: Enables query cache for this command.
  @param int $duration the number of seconds that query result of this command can remain valid in the cache.
  If this is not set, the value of [[Connection::queryCacheDuration]] will be used instead.
  Use 0 to indicate that the cached data will never expire.
  @param \yii\caching\Dependency $dependency the cache dependency associated with the cached query result.
  @return $this the command object itself