How to use DI in a fixture class - symfony

Question

I want to create a fixture for categories, but I get the error
Could you elaborate on how di works in Symfony. The documentation didn't tell me much.
in config / services.yaml the standard code is already specified which seems to solve the di problem
class CategoryFixtures extends \Doctrine\Bundle\FixturesBundle\Fixture
{
private $category;
public function __construct(
\App\Entity\Category $category
) {
$this->category = $category;
}
public function load(\Doctrine\Persistence\ObjectManager $manager)
{
$this->addMainCategories($manager);
}
private function addMainCategories($manager) {
$mainCategoriesArray = ['111', '222', '333', '444', '555'];
foreach ($mainCategoriesArray as $categoryName) {
$this->category->setName($categoryName);
$manager->persist($this->category);
}
$manager->flush();
}
}
Error
Cannot autowire service "App\DataFixtures\CategoryFixtures": argument "$category" of method "__construct()" references class "App\Entity\Category" but no such service exists.

Answer 1

DI isn't really the issue here.
Untested code to create 5 Category entities:
use App\Entity\Category;
use Doctrine\Common\DataFixtures\AbstractFixture;
use Doctrine\Persistence\ObjectManager;
// Creates Category entities Category0, Category1...
class CategoryFixtures extends AbstractFixture
{
private $mainCategoriesArray = ['111', '222', '333', '444', '555'];
public function load(ObjectManager $manager)
{
for ($i = 0; $i < 5; $i++) {
$name = 'Category' . $i;
$$name = new Category();
$$name->setName($this->mainCategoriesArray[$i]);
$manager->persist($$name);
}
$manager->flush();
}
}