about Bulk inserts,

[langziyang]

about bluk import to database, For example i have 100000 item need save and only can use new Entity().this is working code:

public function insertBooks(){
  $result = [1, 2, 3, 1, 2, 3, 4];
  $count = 0;
  foreach ($result as $item) {
      $key = '书' . $item;
      $book = new Book();
      $category = $this->em->getRepository(Category::class)->find($item);//find is dynamic,not only by id
      $book
          ->setName($key)
          ->setCategory($category);
      $this->em->persist($book);
      if ($count % 2 === 0) {
          $this->em->flush();
          $this->em->clear();
      }
      $count++;
  }
  $this->em->flush();
}

so i think if i have 100000 items, then i need fetch 100000 times database to find category. or if i have 4 association，then will fetch 100000*4 times? then i change my code:

private function insertBooks()
{
    $categories = [];
    $result = $this->em->getRepository(Category::class)->findAll();
    foreach ($result as $item) {
        $categories[$item->getId()] = $item;
    }
    $result = [1, 2, 3, 1, 2, 3, 4];
    $count = 0;
    foreach ($result as $item) {
        $key = '书' . $item;
        $book = new Book();
        $category=$categories[$item];//the is dynamic or by other logic
        $book
            ->setName($key)
            ->setCategory($category);
        $this->em->persist($book);
        if ($count % 2 === 0) {
            $this->em->flush();
            $this->em->clear();
        }
        $count++;
    }
    $this->em->flush();
}

then i get error:

A new entity was found through the relationship 'App\Entity\Book#category' that was not configured to cascade persist operations for entity: 分类1. To solve this issue: Either explicitly call EntityManager#persist() on this unknown entity or configure cascade persist this association in the mapping for example @ManyToOne(..,cascade={"persist"})

so , What is the correct approach？