gistfile1.php

<?php
namespace Application\Entity;

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

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

    /**
     * @ORM\OneToMany(targetEntity="Application\Entity\Tag", mappedBy="blogPost")
     */
    protected $tags;

    /**
     * Never forget to initialize all your collections !
     */
    public function __construct()
    {
        $this->tags = new ArrayCollection();
    }

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

    public function addTag(Tag $tag)
    {
        $this->tags->add($tag);
    }

    public function getTags()
    {
        return $this->tags;
    }
}

namespace Application\Entity;

use Doctrine\ORM\Mapping as ORM;

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

    /**
     * @ORM\ManyToOne(targetEntity="Application\Entity\BlogPost", inversedBy="tags")
     */
    protected $blogPost;

    /**
     * @ORM\Content(type="string")
     */
    protected $name;

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

    public function setBlogPost(BlogPost $blogPos)
    {
        $this->blogPost = $blogPost;
    }

    public function getBlogPost()
    {
        return $this->blogPost;
    }

    public function setName($name)
    {
        $this->name = $name;
    }

    public function getName()
    {
        return $this->name;
    }
}