/**
* Get the key for an standard index
*
* @param Index $index Index belonging to entity
* @param string $key Index key
* @return string
*/
public function getIndexKey(Index $index, $key)
{
// idx:article:slug:some-slug
return static::INDEX_NAMESPACE . $this->delimiter . $index->getTableName() . $this->delimiter . $index->getName() . $this->delimiter . $key;
}