code: public function createAttachedEntity($entityClass, $values = [], $key = null)
      {
          if (is_string($values)) {
              $key = $values;
              $values = [];
          }
  
          $entity = $this->repositories->getRepository($entityClass)->create($values);
  
          $this->addAttachedEntity($entity, $key);
  
          return $entity;
      }
docs: Creates an entity and adds it.
  
  @param string        $entityClass
  @param array|string  $values
  @param null|string   $key
  
  @return \Core\Entity\EntityInterface
  @since 0.29