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12.

ManyToMany Relationship

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ManyToMany Relationship

I want you to attend my event! So, you are going to need to be able to RSVP.

Adding a ManyToMany Relationship

First, think about how this would be stored in the database. One user should be able to attend many events, and one event will have many attendees. This is a classic ManyToMany relationship between the Event and User entities.

We already added a ManyToOne relationship earlier and adding a ManyToMany will be very similar.

To model this, create a new attendees property on Event that’ll hold an array of Users that can’t wait to go:

// src/Yoda/EventBundle/Entity/Event.php
// ...

protected $attendees;

Like with a ManyToOne, we just need an annotation that tells Doctrine what type of association this is and what entity it relates to:

// src/Yoda/EventBundle/Entity/Event.php
// ...

/**
 * @ORM\ManyToMany(targetEntity="Yoda\UserBundle\Entity\User")
 */
protected $attendees;

Whenever you have a relationship that holds multiple things, you need to add a __construct method and initialize it to an ArrayCollection:

// src/Yoda/EventBundle/Entity/Event.php
// ...

use Doctrine\Common\Collections\ArrayCollection;
// ...

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

We saw this on the User.events property earlier when we added the OneToMany association.

Next, we’ll add a getter method only - I’ll explain why the setter isn’t needed in a moment:

// src/Yoda/EventBundle/Entity/Event.php
// ...

public function getAttendees()
{
    return $this->attendees;
}

And that’s it! Let’s dump the schema update to see how this will change our database:

php app/console doctrine:schema:update --dump-sql

CREATE TABLE event_user (
    event_id INT NOT NULL,
    user_id INT NOT NULL,
    INDEX IDX_92589AE271F7E88B (event_id),
    INDEX IDX_92589AE2A76ED395 (user_id),
    PRIMARY KEY(event_id, user_id))
    DEFAULT CHARACTER SET utf8 COLLATE utf8_unicode_ci ENGINE = InnoDB;
ALTER TABLE event_user
    ADD CONSTRAINT FK_92589AE271F7E88B FOREIGN KEY (event_id)
    REFERENCES yoda_event (id) ON DELETE CASCADE;
ALTER TABLE event_user
    ADD CONSTRAINT FK_92589AE2A76ED395 FOREIGN KEY (user_id)
    REFERENCES yoda_user (id) ON DELETE CASCADE;

Doctrine is smart enough to know that we need a new “join table” that has event_id and user_id properties. When we relate an Event to a User, it’ll insert a new row in this table for us. Doctrine will handle all of those ugly details.

Re-run the command with --force to add the table:

php app/console doctrine:schema:update --force

The Optional JoinTable

With a ManyToMany, you can optionally add a JoinTable annotation. Add this only if you want to customize something about the join table. For example, you can control the onDelete behavior that happens if a User or Event is deleted:

// src/Yoda/EventBundle/Entity/Event.php
// ...

/**
 * @ORM\ManyToMany(targetEntity="Yoda\UserBundle\Entity\User")
 * @ORM\JoinTable(
 *      joinColumns={@ORM\JoinColumn(onDelete="CASCADE")},
 *      inverseJoinColumns={@ORM\JoinColumn(onDelete="CASCADE")}
 * )
 */
protected $attendees;

Run the doctrine:schema:update command again.

php app/console doctrine:schema:update --dump-sql

Actually, no changes are needed: Doctrine uses this onDelete behavior by default.