How to Embed a Collection of Forms

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In this article, you'll learn how to create a form that embeds a collection of many other forms. This could be useful, for example, if you had a Task class and you wanted to edit/create/remove many Tag objects related to that Task, right inside the same form.

Note

In this article, it's loosely assumed that you're using Doctrine as your database store. But if you're not using Doctrine (e.g. Propel or just a database connection), it's all very similar. There are only a few parts of this tutorial that really care about "persistence".

If you are using Doctrine, you'll need to add the Doctrine metadata, including the ManyToMany association mapping definition on the Task's tags property.

First, suppose that each Task belongs to multiple Tag objects. Start by creating a simple Task class:

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        // src/AppBundle/Entity/Task.php
namespace AppBundle\Entity;

use Doctrine\Common\Collections\ArrayCollection;

class Task
{
    protected $description;

    protected $tags;

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

    public function getDescription()
    {
        return $this->description;
    }

    public function setDescription($description)
    {
        $this->description = $description;
    }

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

Note

The ArrayCollection is specific to Doctrine and is basically the same as using an array (but it must be an ArrayCollection if you're using Doctrine).

Now, create a Tag class. As you saw above, a Task can have many Tag objects:

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        // src/AppBundle/Entity/Tag.php
namespace AppBundle\Entity;

class Tag
{
    private $name;

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

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

Then, create a form class so that a Tag object can be modified by the user:

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        // src/AppBundle/Form/Type/TagType.php
namespace AppBundle\Form\Type;

use AppBundle\Entity\Tag;
use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\OptionsResolver\OptionsResolver;

class TagType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder->add('name');
    }

    public function configureOptions(OptionsResolver $resolver)
    {
        $resolver->setDefaults(array(
            'data_class' => Tag::class,
        ));
    }
}
    

With this, you have enough to render a tag form by itself. But since the end goal is to allow the tags of a Task to be modified right inside the task form itself, create a form for the Task class.

Notice that you embed a collection of TagType forms using the CollectionType field:

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        // src/AppBundle/Form/Type/TaskType.php
namespace AppBundle\Form\Type;

use AppBundle\Entity\Task;
use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\OptionsResolver\OptionsResolver;
use Symfony\Component\Form\Extension\Core\Type\CollectionType;

class TaskType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder->add('description');

        $builder->add('tags', CollectionType::class, array(
            'entry_type' => TagType::class,
            'entry_options' => array('label' => false),
        ));
    }

    public function configureOptions(OptionsResolver $resolver)
    {
        $resolver->setDefaults(array(
            'data_class' => Task::class,
        ));
    }
}
    

In your controller, you'll create a new form from the TaskType:

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        // src/AppBundle/Controller/TaskController.php
namespace AppBundle\Controller;

use AppBundle\Entity\Task;
use AppBundle\Entity\Tag;
use AppBundle\Form\Type\TaskType;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Bundle\FrameworkBundle\Controller\Controller;

class TaskController extends Controller
{
    public function newAction(Request $request)
    {
        $task = new Task();

        // dummy code - this is here just so that the Task has some tags
        // otherwise, this isn't an interesting example
        $tag1 = new Tag();
        $tag1->setName('tag1');
        $task->getTags()->add($tag1);
        $tag2 = new Tag();
        $tag2->setName('tag2');
        $task->getTags()->add($tag2);
        // end dummy code

        $form = $this->createForm(TaskType::class, $task);

        $form->handleRequest($request);

        if ($form->isSubmitted() && $form->isValid()) {
            // ... maybe do some form processing, like saving the Task and Tag objects
        }

        return $this->render('task/new.html.twig', array(
            'form' => $form->createView(),
        ));
    }
}
    

The corresponding template is now able to render both the description field for the task form as well as all the TagType forms for any tags that are already related to this Task. In the above controller, I added some dummy code so that you can see this in action (since a Task has zero tags when first created).

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        {# app/Resources/views/task/new.html.twig #}

{# ... #}

{{ form_start(form) }}
    {# render the task's only field: description #}
    {{ form_row(form.description) }}

    <h3>Tags</h3>
    <ul class="tags">
        {# iterate over each existing tag and render its only field: name #}
        {% for tag in form.tags %}
            <li>{{ form_row(tag.name) }}</li>
        {% endfor %}
    </ul>
{{ form_end(form) }}

{# ... #}
    

When the user submits the form, the submitted data for the tags field are used to construct an ArrayCollection of Tag objects, which is then set on the tag field of the Task instance.

The tags collection is accessible naturally via $task->getTags() and can be persisted to the database or used however you need.

So far, this works great, but this doesn't allow you to dynamically add new tags or delete existing tags. So, while editing existing tags will work great, your user can't actually add any new tags yet.

Caution

In this article, you embed only one collection, but you are not limited to this. You can also embed nested collection as many levels down as you like. But if you use Xdebug in your development setup, you may receive a Maximum function nesting level of '100' reached, aborting! error. This is due to the xdebug.max_nesting_level PHP setting, which defaults to 100.

This directive limits recursion to 100 calls which may not be enough for rendering the form in the template if you render the whole form at once (e.g form_widget(form)). To fix this you can set this directive to a higher value (either via a php.ini file or via ini_set, for example in app/autoload.php) or render each form field by hand using form_row().

Allowing "new" Tags with the "Prototype"

Allowing the user to dynamically add new tags means that you'll need to use some JavaScript. Previously you added two tags to your form in the controller. Now let the user add as many tag forms as they need directly in the browser. This will be done through a bit of JavaScript.

The first thing you need to do is to let the form collection know that it will receive an unknown number of tags. So far you've added two tags and the form type expects to receive exactly two, otherwise an error will be thrown: This form should not contain extra fields. To make this flexible, add the allow_add option to your collection field:

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        // src/AppBundle/Form/Type/TaskType.php

// ...
use Symfony\Component\Form\FormBuilderInterface;

public function buildForm(FormBuilderInterface $builder, array $options)
{
    $builder->add('description');

    $builder->add('tags', CollectionType::class, array(
        'entry_type' => TagType::class,
        'entry_options' => array('label' => false),
        'allow_add' => true,
    ));
}
    

In addition to telling the field to accept any number of submitted objects, the allow_add also makes a "prototype" variable available to you. This "prototype" is a little "template" that contains all the HTML to be able to render any new "tag" forms. To render it, make the following change to your template:

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        <ul class="tags" data-prototype="{{ form_widget(form.tags.vars.prototype)|e('html_attr') }}">
    ...
</ul>
    

Note

If you render your whole "tags" sub-form at once (e.g. form_row(form.tags)), then the prototype is automatically available on the outer div as the data-prototype attribute, similar to what you see above.

Tip

The form.tags.vars.prototype is a form element that looks and feels just like the individual form_widget(tag) elements inside your for loop. This means that you can call form_widget(), form_row() or form_label() on it. You could even choose to render only one of its fields (e.g. the name field):

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        {{ form_widget(form.tags.vars.prototype.name)|e }}
    

On the rendered page, the result will look something like this:

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        <ul class="tags" data-prototype="&lt;div&gt;&lt;label class=&quot; required&quot;&gt;__name__&lt;/label&gt;&lt;div id=&quot;task_tags___name__&quot;&gt;&lt;div&gt;&lt;label for=&quot;task_tags___name___name&quot; class=&quot; required&quot;&gt;Name&lt;/label&gt;&lt;input type=&quot;text&quot; id=&quot;task_tags___name___name&quot; name=&quot;task[tags][__name__][name]&quot; required=&quot;required&quot; maxlength=&quot;255&quot; /&gt;&lt;/div&gt;&lt;/div&gt;&lt;/div&gt;">
    

The goal of this section will be to use JavaScript to read this attribute and dynamically add new tag forms when the user clicks a "Add a tag" link. To make things simple, this example uses jQuery and assumes you have it included somewhere on your page.

Add a script tag somewhere on your page so you can start writing some JavaScript.

First, add a link to the bottom of the "tags" list via JavaScript. Second, bind to the "click" event of that link so you can add a new tag form (addTagForm() will be show next):

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        var $collectionHolder;

// setup an "add a tag" link
var $addTagButton = $('<button type="button" class="add_tag_link">Add a tag</button>');
var $newLinkLi = $('<li></li>').append($addTagButton);

jQuery(document).ready(function() {
    // Get the ul that holds the collection of tags
    $collectionHolder = $('ul.tags');

    // add the "add a tag" anchor and li to the tags ul
    $collectionHolder.append($newLinkLi);

    // count the current form inputs we have (e.g. 2), use that as the new
    // index when inserting a new item (e.g. 2)
    $collectionHolder.data('index', $collectionHolder.find(':input').length);

    $addTagButton.on('click', function(e) {
        // add a new tag form (see next code block)
        addTagForm($collectionHolder, $newLinkLi);
    });
});
    

The addTagForm() function's job will be to use the data-prototype attribute to dynamically add a new form when this link is clicked. The data-prototype HTML contains the tag text input element with a name of task[tags][__name__][name] and id of task_tags___name___name. The __name__ is a little "placeholder", which you'll replace with a unique, incrementing number (e.g. task[tags][3][name]).

The actual code needed to make this all work can vary quite a bit, but here's one example:

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        function addTagForm($collectionHolder, $newLinkLi) {
    // Get the data-prototype explained earlier
    var prototype = $collectionHolder.data('prototype');

    // get the new index
    var index = $collectionHolder.data('index');

    var newForm = prototype;
    // You need this only if you didn't set 'label' => false in your tags field in TaskType
    // Replace '__name__label__' in the prototype's HTML to
    // instead be a number based on how many items we have
    // newForm = newForm.replace(/__name__label__/g, index);

    // Replace '__name__' in the prototype's HTML to
    // instead be a number based on how many items we have
    newForm = newForm.replace(/__name__/g, index);

    // increase the index with one for the next item
    $collectionHolder.data('index', index + 1);

    // Display the form in the page in an li, before the "Add a tag" link li
    var $newFormLi = $('<li></li>').append(newForm);
    $newLinkLi.before($newFormLi);
}
    

Note

It is better to separate your JavaScript in real JavaScript files than to write it inside the HTML as is done here.

Now, each time a user clicks the Add a tag link, a new sub form will appear on the page. When the form is submitted, any new tag forms will be converted into new Tag objects and added to the tags property of the Task object.

Allowing Tags to be Removed

The next step is to allow the deletion of a particular item in the collection. The solution is similar to allowing tags to be added.

Start by adding the allow_delete option in the form Type:

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        // src/AppBundle/Form/Type/TaskType.php

// ...
public function buildForm(FormBuilderInterface $builder, array $options)
{
    // ...

    $builder->add('tags', CollectionType::class, array(
        // ...
        'allow_delete' => true,
    ));
}
    

Now, you need to put some code into the removeTag() method of Task:

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        // src/AppBundle/Entity/Task.php

// ...
class Task
{
    // ...

    public function removeTag(Tag $tag)
    {
        $this->tags->removeElement($tag);
    }
}
    

Template Modifications

The allow_delete option means that if an item of a collection isn't sent on submission, the related data is removed from the collection on the server. In order for this to work in an HTML form, you must remove the DOM element for the collection item to be removed, before submitting the form.

First, add a "delete this tag" link to each tag form:

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        jQuery(document).ready(function() {
    // Get the ul that holds the collection of tags
    $collectionHolder = $('ul.tags');

    // add a delete link to all of the existing tag form li elements
    $collectionHolder.find('li').each(function() {
        addTagFormDeleteLink($(this));
    });

    // ... the rest of the block from above
});

function addTagForm() {
    // ...

    // add a delete link to the new form
    addTagFormDeleteLink($newFormLi);
}
    

The addTagFormDeleteLink() function will look something like this:

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        function addTagFormDeleteLink($tagFormLi) {
    var $removeFormButton = $('<button type="button">Delete this tag</button>');
    $tagFormLi.append($removeFormButton);

    $removeFormButton.on('click', function(e) {
        // remove the li for the tag form
        $tagFormLi.remove();
    });
}
    

When a tag form is removed from the DOM and submitted, the removed Tag object will not be included in the collection passed to setTags(). Depending on your persistence layer, this may or may not be enough to actually remove the relationship between the removed Tag and Task object.

When removing objects in this way, you may need to do a little bit more work to ensure that the relationship between the Task and the removed Tag is properly removed.

In Doctrine, you have two sides of the relationship: the owning side and the inverse side. Normally in this case you'll have a many-to-many relationship and the deleted tags will disappear and persist correctly (adding new tags also works effortlessly).

But if you have a one-to-many relationship or a many-to-many relationship with a mappedBy on the Task entity (meaning Task is the "inverse" side), you'll need to do more work for the removed tags to persist correctly.

In this case, you can modify the controller to remove the relationship on the removed tag. This assumes that you have some editAction() which is handling the "update" of your Task:

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        // src/AppBundle/Controller/TaskController.php

use AppBundle\Entity\Task;
use Doctrine\Common\Collections\ArrayCollection;

// ...
public function editAction($id, Request $request)
{
    $entityManager = $this->getDoctrine()->getManager();
    $task = $entityManager->getRepository(Task::class)->find($id);

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

    $originalTags = new ArrayCollection();

    // Create an ArrayCollection of the current Tag objects in the database
    foreach ($task->getTags() as $tag) {
        $originalTags->add($tag);
    }

    $editForm = $this->createForm(TaskType::class, $task);

    $editForm->handleRequest($request);

    if ($editForm->isValid()) {

        // remove the relationship between the tag and the Task
        foreach ($originalTags as $tag) {
            if (false === $task->getTags()->contains($tag)) {
                // remove the Task from the Tag
                $tag->getTasks()->removeElement($task);

                // if it was a many-to-one relationship, remove the relationship like this
                // $tag->setTask(null);

                $entityManager->persist($tag);

                // if you wanted to delete the Tag entirely, you can also do that
                // $entityManager->remove($tag);
            }
        }

        $entityManager->persist($task);
        $entityManager->flush();

        // redirect back to some edit page
        return $this->redirectToRoute('task_edit', array('id' => $id));
    }

    // render some form template
}
    

As you can see, adding and removing the elements correctly can be tricky. Unless you have a many-to-many relationship where Task is the "owning" side, you'll need to do extra work to make sure that the relationship is properly updated (whether you're adding new tags or removing existing tags) on each Tag object itself.

The jQuery plugin symfony-collection helps with collection form elements, by providing the JavaScript functionality needed to add, edit and delete elements of the collection. More advanced functionality like moving or duplicating an element in the collection and customizing the buttons is also possible.

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.

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