Es gibt zwei Instanzen zum Bloggen und Kommentieren:

• blog.comments speichert den Kommentartyp
• comment.blog_id ist der Fremdschlüssel von Blog

Meine Abfrageaussage:

public function getLatestBlogs($limit=null){
    $qb = $this->createQueryBuilder('b')
        ->select('b','c')
        ->leftJoin('b.comments', 'c')
        ->addOrderBy('b.created', 'DESC')
    ;

    if (false === is_null($limit))
        $qb->setMaxResults($limit);

    return $qb->getQuery()->getResult(\Doctrine\ORM\Query::HYDRATE_OBJECT);
}

Fehlermeldung:

Error: Call to a member function add() on a non-object in E:\xampp\htdocs\symfony\vendor\doctrine\orm\lib\Doctrine\ORM\PersistentCollection.php line 177
500 Internal Server Error - FatalErrorException 

Kommentieren Sie den Hauptcode, der Rest wird generiert

/**
 * Class Comment
 * @ORM\Entity(repositoryClass="Blogger\BlogBundle\Entity\CommentRepository")
 * @ORM\Table(name="comment")
 * @ORM\HasLifecycleCallbacks()
 */
class Comment{
    /**
     * @ORM\Id
     * @ORM\Column(type="integer")
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    protected $id;

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

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

    /**
     * @ORM\Column(type="boolean")
     */
    protected $approved;

    /**
     * @ORM\ManyToOne(targetEntity="Blog",inversedBy="comments")
     * @ORM\JoinColumn(name="blog_id",referencedColumnName="id")
     */
    protected $blog;

    /**
     * @ORM\Column(type="datetime")
     */
    protected $created;

    /**
     * @ORM\Column(type="datetime")
     */
    protected $updated;

 }

Blog-Hauptcode:

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

/**
 * @ORM\Column(type="string")
 */
protected $title;

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

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

/**
 * @var
 * @ORM\Column(type="string",length=20)
 */
protected $image;

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

/**
 * @ORM\OneToMany(targetEntity="Comment",mappedBy="blog")
 */
protected $comments = array();

/**
 * @var
 * @ORM\Column(type="datetime")
 */
protected $created;

/**
 * @var
 * @ORM\Column(type="datetime")
 */
protected $updated;