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Saving the Inverse Side of a ManyToMany

Back on the main part of the site, click one of the genuses, and then click one of the users that studies it. This page has a little edit button: click that. Welcome to a very simple User form.

Building the Field

Ok, same plan: add checkboxes so that I can choose which genuses are being studied by this User. Open the controller: UserController and find editAction():

81 lines src/AppBundle/Controller/UserController.php
... lines 1 - 5
use AppBundle\Form\UserEditForm;
... lines 7 - 11
class UserController extends Controller
{
... lines 14 - 57
public function editAction(User $user, Request $request)
{
$form = $this->createForm(UserEditForm::class, $user);
... lines 61 - 78
}
}

This uses UserEditForm, so go open that as well.

In buildForm(), we'll do the exact same thing we did on the genus form: add a new field called studiedGenuses - that's the property name on User that we want to modify:

41 lines src/AppBundle/Form/UserEditForm.php
... lines 1 - 6
use Symfony\Bridge\Doctrine\Form\Type\EntityType;
... lines 8 - 14
class UserEditForm extends AbstractType
{
public function buildForm(FormBuilderInterface $builder, array $options)
{
$builder
... lines 20 - 24
->add('studiedGenuses', EntityType::class, [
... lines 26 - 29
])
;
}
... lines 33 - 39
}

Keep going: use EntityType::class and then set the options: class set now to Genus::class to make Genus checkboxes. Then, multiple set to true, expanded set to true, and choice_label set to name to display that field from Genus:

41 lines src/AppBundle/Form/UserEditForm.php
... lines 1 - 6
use Symfony\Bridge\Doctrine\Form\Type\EntityType;
... lines 8 - 14
class UserEditForm extends AbstractType
{
public function buildForm(FormBuilderInterface $builder, array $options)
{
$builder
... lines 20 - 24
->add('studiedGenuses', EntityType::class, [
'class' => Genus::class,
'multiple' => true,
'expanded' => true,
'choice_label' => 'name',
])
;
}
... lines 33 - 39
}

Next! Open the template: user/edit.html.twig. At the bottom, use form_row(userForm.studiedGenuses):

25 lines app/Resources/views/user/edit.html.twig
... lines 1 - 2
{% block body %}
<div class="container">
<div class="row">
<div class="col-xs-8">
... lines 7 - 8
{{ form_start(userForm) }}
... lines 10 - 16
{{ form_row(userForm.studiedGenuses) }}
... lines 18 - 19
{{ form_end(userForm) }}
</div>
</div>
</div>
{% endblock %}

That's it.

Try it! Refresh! Cool! This User is studying five genuses: good for them! Let's uncheck one genus, check a new one and hit Update.

It didn't Work!!! Inverse Relationships are Read-Only

Wait! It didn't work! The checkboxes just reverted back! What's going on!?

This is the moment where someone who doesn't know what we're about to learn, starts to hate Doctrine relations.

Earlier, we talked about how every relationship has two sides. You can start with a Genus and talk about the genus scientist users related to it:

197 lines src/AppBundle/Entity/Genus.php
... lines 1 - 14
class Genus
{
... lines 17 - 71
/**
* @ORM\ManyToMany(targetEntity="User", inversedBy="studiedGenuses", fetch="EXTRA_LAZY")
* @ORM\JoinTable(name="genus_scientist")
*/
private $genusScientists;
... lines 77 - 195
}

Or, you can start with a User and talk about its studied genuses:

224 lines src/AppBundle/Entity/User.php
... lines 1 - 16
class User implements UserInterface
{
... lines 19 - 77
/**
* @ORM\ManyToMany(targetEntity="Genus", mappedBy="genusScientists")
* @ORM\OrderBy({"name" = "ASC"})
*/
private $studiedGenuses;
... lines 83 - 222
}

Only one of these side - in this case the Genus - is the owning side. So far, that hasn't meant anything: we can easily read data from either direction. BUT! The owning side has one special power: it is the only side that you're allowed to change.

What I mean is, if you have a User object and you add or remove genuses from its studiedGenuses property and save... Doctrine will do nothing. Those changes are completely ignored.

And it's not a bug! Doctrine is built this way on purpose. The data about which Genuses are linked to which Users is stored in two places. So Doctrine needs to choose one of them as the official source when it saves. It uses the owning side.

For a ManyToMany relationship, we chose the owning side when we set the mappedBy and inversedBy options. The owning side is also the only side that's allowed to have the @ORM\JoinTable annotation.

This is a long way of saying that if we want to update this relationship, we must add and remove users from the $genusScientists property on Genus:

197 lines src/AppBundle/Entity/Genus.php
... lines 1 - 14
class Genus
{
... lines 17 - 71
/**
* @ORM\ManyToMany(targetEntity="User", inversedBy="studiedGenuses", fetch="EXTRA_LAZY")
* @ORM\JoinTable(name="genus_scientist")
*/
private $genusScientists;
... lines 77 - 195
}

Adding and removing genuses from the User object will do nothing. And that's exactly what our form just did.

No worries! We can fix this, with just a little bit of really smart code.

Leave a comment!

  • 2017-07-31 Victor Bocharsky

    Hey Dave,

    Sorry for misleading you. Actually, we have an issue about this, but it's not prioritized yet. But for now, you can use our handy expandable code block below each video. You can even expand the entire file by pressing "Show All Lines" button (double arrows in the left top corner of each code block) to get more context. Plus, keep in mind "Copy" button in the right top corner, it prevent you to select the code manually.

    Cheers!

  • 2017-07-28 Dave Wilson

    I couldn't find any of the code to save the inverse many-to-many. I understand now that the finish folder is the end of this whole course, not this chapter. At the end of this course the many-to-many is turned into a one-to-many / many-to-one so that's why it's not there. Sorry for my misunderstanding, although it would be nice to have the code after each chapter since things keep changing.

  • 2017-07-28 Victor Bocharsky

    Hay Dave,

    What exactly can't you find in the "finish/" folder?

    Cheers!

  • 2017-07-28 Dave Wilson

    Where is this in the ''finish' code folder?