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13.

Using the ManyToMany so Users can Attend an Event

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Using the ManyToMany so Users can Attend an Event

Let’s put our new relationship into action. Create two new routes next to our other event routes: one for attending an event and another for unattending:

# src/Yoda/EventBundle/Resources/config/routing/event.yml
# ...

event_attend:
    pattern:  /{id}/attend
    defaults: { _controller: "EventBundle:Event:attend" }

event_unattend:
    pattern:  /{id}/unattend
    defaults: { _controller: "EventBundle:Event:unattend" }

Next, hop into the EventController and create the two corresponding action methods:

// src/Yoda/EventBundle/Controller/EventController.php
// ...

public function attendAction($id)
{

}

public function unattendAction($id)
{

}

Start with attendAction. The logic here should feel familiar. First, query for an Event entity. Next, throw a createNotFoundException if no Event is found:

// src/Yoda/EventBundle/Controller/EventController.php
// ...

public function attendAction($id)
{
    $em = $this->getDoctrine()->getManager();
    /** @var $event \Yoda\EventBundle\Entity\Event */
    $event = $em->getRepository('EventBundle:Event')->find($id);

    if (!$event) {
        throw $this->createNotFoundException('No event found for id '.$id);
    }

    // ... todo
}

All we need to do now is add the current User object as an attendee on this Event. Remember that the attendees property is actually an ArrayCollection object. Use its add method then save the Event. Finally, redirect when you’re finished:

// src/Yoda/EventBundle/Controller/EventController.php
// ...

public function attendAction($id)
{
    $em = $this->getDoctrine()->getManager();
    /** @var $event \Yoda\EventBundle\Entity\Event */
    $event = $em->getRepository('EventBundle:Event')->find($id);

    if (!$event) {
        throw $this->createNotFoundException('No event found for id '.$id);
    }

    $event->getAttendees()->add($this->getUser());

    $em->persist($event);
    $em->flush();

    $url = $this->generateUrl('event_show', array(
        'slug' => $event->getSlug(),
    ));

    return $this->redirect($url);
}

Notice that we just added an attendee without needing a setAttendees method on Event. This works because attendees is an object, so we can just call getAttendees and then modify it.

Printing Attendees in Twig

Before we try this out, let’s update the event show page. Use the length filter to count the number of attendees, to make sure we make enough guacamole:

{# src/Yoda/EventBundle/Resources/views/Event/show.html.twig #}
{# ... #}

<dt>who:</dt>
<dd>
    {{ entity.attendees|length }} attending!

    <ul class="users">
        <li>nobody yet!</li>
    </ul>
</dd>

We can even loop over the event’s attendees and print each of them out. Print a nice message when nobody’s attending, using Twig’s really nice for-else functionality:

{# src/Yoda/EventBundle/Resources/views/Event/show.html.twig #}
{# ... #}

<dt>who:</dt>
<dd>
    {{ entity.attendees|length }} attending!

    <ul class="users">
        {% for attendee in entity.attendees %}
            <li>{{ attendee }}</li>
        {% else %}
            <li>nobody yet!</li>
        {% endfor %}
    </ul>
</dd>

Now help me add a link to the new event_attend route if the user is logged in:

{# src/Yoda/EventBundle/Resources/views/Event/show.html.twig #}
{# ... #}

<dt>who:</dt>
<dd>
    {# ... #}

    <a href="{{ path('event_attend', {'id': entity.id}) }}" class="btn btn-success btn-xs">
        I totally want to go!
    </a>
</dd>

Testing out the Relationship

Head over to an event in your browser. It says 0 attending. Now click the new link. After the redirect, we see 1 attending, but we also see a huge error:

Catchable Fatal Error: Object of class YodaUserBundleEntityUser could not be converted to string

The fact that we show 1 attending means that the database relationship was stored correctly. We can prove it by querying for the join table:

php app/console doctrine:query:sql "SELECT * FROM event_user"

Yep, we see one row that links our user to this event.

Adding a __toString to User

So what’s the error? Look closely: PHP is trying to convert our User object into a string. This is happening because we’re looping over event.attendees, which gives us User objects that we’re printing:

{# src/Yoda/EventBundle/Resources/views/Event/show.html.twig #}

{% for attendee in entity.attendees %}
    <li>{{ attendee }}</li>
{% else %}
    <li>nobody yet!</li>
{% endfor %}

We have two options to fix this. First, we could just print out a specific property on the User:

{# src/Yoda/EventBundle/Resources/views/Event/show.html.twig #}

{% for attendee in entity.attendees %}
    <li>{{ attendee.username }}</li>
{% else %}
    <li>nobody yet!</li>
{% endfor %}

But if you do just want to print the object, you can add a __toString method to the User class:

// src/Yoda/UserBundle/Entity/User.php
// ...

public function __toString()
{
    return (string) $this->getUsername();
}

Refresh now. Sweet, no errors!

Let’s also take a second and fill in the # of attendees on the index page:

{# src/Yoda/EventBundle/Resources/views/Event/index.html.twig #}
{# ... #}

{% for entity in entities %}
    {# ... #}

    <dt>who:</dt>
    <dd>{{ entity.attendees|length }} attending!</dd>

    {# ... #}
{% endfor %}