@PreUpdate & EmbedMany

// Article
namespace Bundle\ArticleBundle\Document;

use Bundle\CommentBundle\Document\Comment;
use Bundle\ExerciseCommonBundle\Document\Repository;

/**
 * @Document(
 *   collection="article",
 *   indexes={
 *     @Index(keys={"createdAt"="asc"})
 *   },
 *   repositoryClass="Bundle\ArticleBundle\Document\ArticleRepository"
 * )
 * @HasLifecycleCallbacks
 */
class Article
{
    /**
     * @Id
     */
    protected $id;
    /**
     * @ReferenceOne(targetDocument="Bundle\AccountBundle\Document\User")
     */
    protected $user;
    /**
     * @ReferenceOne(targetDocument="Bundle\ArticleBundle\Document\ArticleCategory")
     * @Validation({
     *      @NotBlank (message="Please select a category.")
     * })
     */
    protected $category;
    /**
     * @Field(type="string")
     */
    protected $slug;
    /**
     * @Field(type="string")
     * @Validation({
     *      @NotBlank (message="You forgot a Title?"),
     *      @MinLength(limit=4, message="Just a little too short.")
     * })
     */
    protected $title;
    /**
     * @Field(type="string")
     * @Validation({
     *      @NotBlank (message="Please summarize your article."),
     *      @MinLength(limit=100, message="Not long enough!"),
     *      @MaxLength(limit=200, message="A wee bit too long.")
     * })
     */
    protected $summary;
    /**
     * @Field(type="string")
     * @Validation({
     *      @NotBlank (message="Where's the beef?")
     * })
     */
    protected $body;
    
	/** 
	 * @EmbedMany(targetDocument="Bundle\CommentBundle\Document\Comment") 
	 * */
	protected $comments = array();
	
    /**
     * @Field(type="boolean")
     */
    protected $published = false;
    /**
     * @Field(type="date", nullable=false)
     */
    protected $createdAt;
    /**
     * @Field(type="date", nullable=false)
     */
    protected $updatedAt;

    public function getId()
    {
        return $this->id;
    }

    public function isNew() {
        return empty($this->id);
    }

    public function getUser()
    {
        return $this->user;
    }

    public function getCategory()
    {
        return $this->category;
    }

    public function getSlug()
    {
        return $this->slug;
    }

    public function setSlug($slug)
    {
        $this->slug = $slug;
    }

    public function setUniqueSlug()
    {
        $this->slug = Repository::Slugify($this->title);
    }

    public function isPublished()
    {
        if($this->published) {
            return true;
        }
        return false;
    }

    public function publish()
    {
        $this->published = true;
    }

    public function unpublish()
    {
        $this->published = false;
    }

    public function getSummary()
    {
        return $this->summary;
    }

    public function setSummary($summary)
    {
        $this->summary = $summary;
    }

    public function getTitle()
    {
        return $this->title;
    }

    public function setTitle($title)
    {
        $this->title = $title;
    }

    public function getBody()
    {
        return $this->body;
    }



    public function setBody($body)
    {
        $this->body = $body;
    }

    public function setUser($user) {
        $this->user = $user;
    }

    public function setCategory($category) {
        $this->category = $category;
    }

    public function getCreatedAt()
    {
        return $this->createdAt;
    }

    /**
     * It can be useful when writing fixtures
     * @param \DateTime $date
     * @return void
     */
    public function setCreatedAt(\DateTime $date)
    {
        $this->createdAt = $date;
    }

    public function getUpdatedAt()
    {
        return $this->updatedAt;
    }

    public function __toString()
    {
        return $this->title();
    }
    
    
	/**
	 * @return the $comments
	 */
	public function getComments() {
		return $this->comments;
	}    
    
	/**
	 * @param $comments the $comments to set
	 */
	public function setComments($comments) {
		$this->comments = $comments;
	}
    /** @PrePersist */
    public function incrementCreatedAt()
    {
        if(null === $this->createdAt) {
            $this->createdAt = new \DateTime();
        }
        $this->updatedAt = new \DateTime();
    }

    /** @PreUpdate */
    public function incrementUpdatedAt() {
        $this->updatedAt = new \DateTime();
    }

    public function fromArray(array $array)
    {
        foreach($array as $property => $value) {
            $this->$property = $value;
        }
    }
}

// Comment
<?php

namespace Bundle\CommentBundle\Document;

/**
 * @EmbeddedDocument
 */
class Comment
{
	
	/**
     * @Id
     */
    protected $id;
	
    /**
     * @Field(type="date", nullable=true)
     */
    protected $createdAt;

    /**
     * @Field(type="string", nullable=true)
     */
    protected $message;

    /**
     * @ReferenceOne(targetDocument="Bundle\AccountBundle\Document\User")
     */
    protected $user;

    /**
     * @return the $createdAt
     */
    public function getCreatedAt() {
        return $this->createdAt;
    }

    /**
     * @return the $message
     */
    public function getMessage() {
        return $this->message;
    }

    /**
     * @return the $user
     */
    public function getUser() {
        return $this->user;
    }

    /**
     * @param $createdAt the $createdAt to set
     */
    public function setCreatedAt($createdAt) {
        $this->createdAt = $createdAt;
    }

//    /** @PrePersist */
//    public function incrementCreatedAt()
//    {
//        if(null === $this->createdAt) {
//            $this->createdAt = new \DateTime();
//        }
//        $this->updatedAt = new \DateTime();
//    }
//
//    /** @PreUpdate */
//    public function incrementUpdatedAt() {
//        $this->updatedAt = new \DateTime();
//    }

    /**
     * @param $message the $message to set
     */
    public function setMessage($message) {
        $this->message = $message;
    }

    /**
     * @param $by_user_id the $by_user_id to set
     */
    public function setUser($user) {
        $this->user = $user;
    }
}

                $article = $this->odm->getRepository('Bundle\ArticleBundle\Document\Article')->find("someID");

		$newComment = new Comment();
		$newComment->setUser($user);
		$newComment->setMessage("PPPPOOOOOPPPP");
		$newComment->setCreatedAt(new \DateTime());
		
		$comments = $article->getComments();
		$comments[] = $newComment;
		$article->setComments($comments);
		
		$this->odm->persist($article);
                // With or without the args to flush
		$this->odm->flush(array('safe' => true));