trait EntityOwnerTrait

trait EntityOwnerTrait {
    
    /**
     * Returns an array of base field definitions for entity owners.
     *
     * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
     *   The entity type to add the owner field to.
     *
     * @return \Drupal\Core\Field\BaseFieldDefinition[]
     *   An array of base field definitions.
     *
     * @throws \Drupal\Core\Entity\Exception\UnsupportedEntityTypeDefinitionException
     *   Thrown when the entity type does not implement EntityOwnerInterface or
     *   if it does not have an "owner" entity key.
     */
    public static function ownerBaseFieldDefinitions(EntityTypeInterface $entity_type) {
        if (!is_subclass_of($entity_type->getClass(), EntityOwnerInterface::class)) {
            throw new UnsupportedEntityTypeDefinitionException('The entity type ' . $entity_type->id() . ' does not implement \\Drupal\\user\\EntityOwnerInterface.');
        }
        if (!$entity_type->hasKey('owner')) {
            throw new UnsupportedEntityTypeDefinitionException('The entity type ' . $entity_type->id() . ' does not have an "owner" entity key.');
        }
        return [
            $entity_type->getKey('owner') => BaseFieldDefinition::create('entity_reference')->setLabel(new TranslatableMarkup('User ID'))
                ->setSetting('target_type', 'user')
                ->setTranslatable($entity_type->isTranslatable())
                ->setDefaultValueCallback(static::class . '::getDefaultEntityOwner'),
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function getOwnerId() {
        return $this->getEntityKey('owner');
    }
    
    /**
     * {@inheritdoc}
     */
    public function setOwnerId($uid) {
        $key = $this->getEntityType()
            ->getKey('owner');
        $this->set($key, $uid);
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getOwner() {
        $key = $this->getEntityType()
            ->getKey('owner');
        return $this->get($key)->entity;
    }
    
    /**
     * {@inheritdoc}
     */
    public function setOwner(UserInterface $account) {
        $key = $this->getEntityType()
            ->getKey('owner');
        $this->set($key, $account);
        return $this;
    }
    
    /**
     * Default value callback for 'owner' base field.
     *
     * @return mixed
     *   A default value for the owner field.
     */
    public static function getDefaultEntityOwner() {
        return \Drupal::currentUser()->id();
    }

}