public function getPreviousAccessedColumns()
{
if ($this->cache && $this->previousAccessedColumns === NULL) {
$this->accessedColumns = $this->previousAccessedColumns = $this->cache->load($this->getGeneralCacheKey());
if ($this->previousAccessedColumns === NULL) {
$this->previousAccessedColumns = [];
}
}
return array_keys(array_filter((array) $this->previousAccessedColumns));
}