Symfony2-Doctrine: ManyToMany relation is not saved to database
Your Category entity is the inverse side of the relationship.
Try changing addItems to look like this:
public function addItem(\Ako\StoreBundle\Entity\Item $item) { $item->addCategory($this); $this->items[] = $item; }Note that I changed your plural names to singular, since you're dealing with single entities, not collections.
I had the same problems...I think you forgot
$category->addItems($item);$em->persist($category);$em->flush();