Question

How can i create a relationship between entities with Symfony 2 and Doctrine? I’m only able to create standalone entities. Maybe someone can help me figure this out using the entity generator? I want to:

• Create two entities: Post and Category. A Post is part of a Category.
• Create a Tag entity: A Post can have many Tags.

Answer 1

A practical example is covered in Symfony2 docs here:

http://symfony.com/doc/current/book/doctrine.html#entity-relationships-associations

To elaborate, taking the first example, you need to create a OneToMany relationship between your Category object and your Post object:

Category.php:

<?php

namespace Your\CustomBundle\Entity;

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

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

    /**
     * @ORM\OneToMany(targetEntity="Post", mappedBy="category")
     */
    public $posts;

    /**
     * Constructor
     */
    public function __construct()
    {
        $this->posts = new ArrayCollection();
    }

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

Post.php

<?php

namespace Your\CustomBundle\Entity;

use Doctrine\ORM\Mapping as ORM;

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

    /**
     * @ORM\ManyToOne(targetEntity="Category", inversedBy="posts")
     */
    public $category;

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

This should get you started. I’ve just written this so there might be errors :s

I’m making properties $posts and $category public here for brevity; however you’d probably be advised to make these private and add setters/getters to your classes.

Also note that $posts is an array-like Doctrine ArrayObject class especially for arrgregating entities, with methods like $category->posts->add($post) etc.

For more detail look into association mapping in the Doctrine documentation. You’ll probably need to set up a ManyToMany relationship between Posts and Tags.

Hope this helps 🙂