Shopware 6 custom plugin, deleting extension on delete parent does not work

Question

I have an extension created following the manual Adding complex data to existing entities.
My product has with this extension another property like e.g product_color. On delete the product the prop (entity table) product_color still remains in the database.

// Migration%123%ProductColor.php

...
    public function update(Connection $connection): void
    {
        $sql = <<<SQL
CREATE TABLE `product_color` (
  `id` binary(16) NOT NULL,
  `product_id` binary(16) DEFAULT NULL,
  `color` tinyint(1) NOT NULL DEFAULT '0',
  `created_at` datetime(3) NOT NULL,
  `updated_at` datetime(3) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
SQL;
        $connection->executeStatement($sql);
    }
...

EDIT #1
As recommend by @Alex, i've added flags, but the extension keep in the database:

// custom/plugins/MyPlugin/src/Extension/ProductColor/ProductColorExtension.php

class ProductColorExtension extends EntityExtension
{
    public function extendFields(FieldCollection $collection): void
    {
        $collection
            ->add(
                (new OneToOneAssociationField(
                'productColor',
                'id',
                'product_id',
                ProductColorExtensionDefinition::class,
                true
            ))->addFlags(new CascadeDelete())
            );
    }

    public function getDefinitionClass(): string
    {
        return ProductDefinition::class;
    }
}

Questions:

• how to make the additional property deletable on delete its parent (delete cascade)?
• where are the corresponding manual how to achieve this?

Answer 1

In addition to setting the CascadeDelete flag in the entity definition, you need to add a foreign key constraint with your database migration and use CASCADE for the ON DELETE subclause.

ALTER TABLE `product_color` 
ADD CONSTRAINT `fk.product_color.product_id` FOREIGN KEY (`product_id`) REFERENCES `product` (`id`) ON DELETE CASCADE ON UPDATE CASCADE;