Doctrine join error "Undefined index: product in ObjectHydrator.php" (Symfony2)

Question

I am trying to learn Symfony2 and currently at "8: Entity Relationships/Associations (Joining to Related Records)" of "The Book". Just coded along with the examples (triple checked my code) but then I got this error:

Notice: Undefined index: product in C:\My\Path\vendor\doctrine\lib\Doctrine\ORM\Internal\Hydration\ObjectHydrator.php line 95

This is the my code:

//src\Acme\StoreBundle\Repository\ProductRepository.php
public function findOneByIdJoinedToCategory($id)
{
    $query = $this->getEntityManager()
        ->createQuery('SELECT p, c 
            FROM AcmeStoreBundle:Product p 
            JOIN p.category c 
            WHERE p.id = :id')
        ->setParameter('id', $id);

    try {
        return $query->getSingleResult();
    } catch (\Doctrine\ORM\NoResultException $e) {
        return null;
    }
}

//src\Acme\StoreBundle\Controller\DefaultController.php
public function showAction($id)
{
    $product = $this->getDoctrine()
        ->getRepository('AcmeStoreBundle:Product')
        ->findOneByIdJoinedToCategory($id);

    if (!$product) {
        throw $this->createNotFoundException('No product found for id: '.$id);
    }

    $category = $product->getCategory();

    return $this->render('AcmeStoreBundle:Default:product.html.twig', array(
        'product' => $product,
        'category' => $category)
    );
}

If I use this code everything works like it should:

//src\Acme\StoreBundle\Controller\DefaultController.php
public function showAction($id)
{
    $product = $this->getDoctrine()
        ->getRepository('AcmeStoreBundle:Product')
        ->find($id);

    if (!$product) {
        throw $this->createNotFoundException('No product found for id: '.$id);
    }

    $category = $product->getCategory();

    return $this->render('AcmeStoreBundle:Default:product.html.twig', array(
        'product' => $product,
        'category' => $category)
    );
}

Any ideas?

Edit: Product Entity:

<?php
namespace Acme\StoreBundle\Entity;

use Doctrine\ORM\Mapping as ORM;

class Product
{
/**
 * @ORM\Id
 * @ORM\Column(type="integer")
 * @ORM\GeneratedValue(strategy="AUTO")
 */
protected $id;

/**
 * @ORM\Column(type="string", length=100)
 */
protected $name;

/**
 * @ORM\Column(type="decimal", scale=2)
 */
protected $price;

/**
 * @ORM\Column(type="text")
 */
protected $description;

/**
 * @ORM\Column(type="text", nullable="true")
 */
protected $extras;

/**
 * @ORM\ManyToOne(targetEntity="Category", inversedBy="product")
 * @ORM\JoinColumn(name="category_id", referencedColumnName="id")
 */
protected $category;

/**
 * Get id
 *
 * @return integer 
 */
public function getId()
{
    return $this->id;
}

/**
 * Set name
 *
 * @param string $name
 */
public function setName($name)
{
    $this->name = $name;
}

/**
 * Get name
 *
 * @return string 
 */
public function getName()
{
    return $this->name;
}

/**
 * Set price
 *
 * @param decimal $price
 */
public function setPrice($price)
{
    $this->price = $price;
}

/**
 * Get price
 *
 * @return decimal 
 */
public function getPrice()
{
    return $this->price;
}

/**
 * Set description
 *
 * @param text $description
 */
public function setDescription($description)
{
    $this->description = $description;
}

/**
 * Get description
 *
 * @return text 
 */
public function getDescription()
{
    return $this->description;
}

/**
 * Set extras
 *
 * @param text $extras
 */
public function setExtras($extras)
{
    $this->extras = $extras;
}

/**
 * Get extras
 *
 * @return text 
 */
public function getExtras()
{
    return $this->extras;
}

/**
 * Set category
 *
 * @param Acme\StoreBundle\Entity\Category $category
 */
public function setCategory(\Acme\StoreBundle\Entity\Category $category)
{
    $this->category = $category;
}

/**
 * Get category
 *
 * @return Acme\StoreBundle\Entity\Category 
 */
public function getCategory()
{
    return $this->category;
}
}

Category entity:

<?php

namespace Acme\StoreBundle\Entity;

use Doctrine\ORM\Mapping as ORM;
use Doctrine\Common\Collections\ArrayCollection;

/**
 * Acme\StoreBundle\Entity\Category
 *
 * @ORM\Table()
 * @ORM\Entity
 */
class Category
{
/**
 * @var integer $id
 *
 * @ORM\Column(name="id", type="integer")
 * @ORM\Id
 * @ORM\GeneratedValue(strategy="AUTO")
 */
private $id;

/**
 * @var string $name
 *
 * @ORM\Column(name="name", type="string", length=255)
 */
private $name;

/**
 * @ORM\OneToMany(targetEntity="Product", mappedBy="category")
 */
protected $products;

public function __construct()
{
    $this->products = new ArrayCollection();
}

/**
 * Get id
 *
 * @return integer 
 */
public function getId()
{
    return $this->id;
}

/**
 * Set name
 *
 * @param string $name
 */
public function setName($name)
{
    $this->name = $name;
}

/**
 * Get name
 *
 * @return string 
 */
public function getName()
{
    return $this->name;
}

/**
 * Add products
 *
 * @param Acme\StoreBundle\Entity\Product $products
 */
public function addProduct(\Acme\StoreBundle\Entity\Product $products)
{
    $this->products[] = $products;
}

/**
 * Get products
 *
 * @return Doctrine\Common\Collections\Collection 
 */
public function getProducts()
{
    return $this->products;
}
}

Answer 1

OK. Your problem is that you are saying in the Product entity that the category relationship is inversed by "product" and it should be "products". Just change it to

/**
 * @ORM\ManyToOne(targetEntity="Category", inversedBy="products")
 * @ORM\JoinColumn(name="category_id", referencedColumnName="id")
 */
protected $category;

and it should work