Live Components

EXPERIMENTAL This component is currently experimental and is likely to change, or even change drastically.

Live components work with the TwigComponent library to give you the power to automatically update your Twig components on the frontend as the user interacts with them. Inspired by Livewire and Phoenix LiveView.

A real-time product search component might look like this:

// src/Components/ProductSearchComponent.php
namespace App\Components;

use Symfony\UX\LiveComponent\Attribute\AsLiveComponent;
use Symfony\UX\LiveComponent\DefaultActionTrait;

#[AsLiveComponent('product_search')]
class ProductSearchComponent
{
    use DefaultActionTrait;

    public string $query = '';

    private ProductRepository $productRepository;

    public function __construct(ProductRepository $productRepository)
    {
        $this->productRepository = $productRepository;
    }

    public function getProducts(): array
    {
        // example method that returns an array of Products
        return $this->productRepository->search($this->query);
    }
}

{# templates/components/product_search.html.twig #}
<div {{ init_live_component(this) }}>
    <input
        type="search"
        name="query"
        value="{{ this.query }}"
        data-action="live#update"
    >

    <ul>
        {% for product in this.products %}
            <li>{{ product.name }}</li>
        {% endfor %}
    </ul>
</div>

As a user types into the box, the component will automatically re-render and show the new results!

Want a demo? Check out https://github.com/weaverryan/live-demo.

Installation

Let's get started! Install the library with:

composer require symfony/ux-live-component

This comes with an embedded JavaScript Stimulus controller. Unlike other Symfony UX packages, this needs to be enabled manually in your config/bootstrap.js file:

// config/bootstrap.js
import LiveController from '@symfony/ux-live-component';
import '@symfony/ux-live-component/styles/live.css';
// ...

app.register('live', LiveController);

Finally, reinstall your Node dependencies and restart Encore:

yarn install --force
yarn encore dev

Oh, and just one more step! Import a routing file from the bundle:

# config/routes.yaml
live_component:
    resource: '@LiveComponentBundle/Resources/config/routing/live_component.xml'

That's it! We're ready!

Making your Component "Live"

If you haven't already, check out the Twig Component documentation to get the basics of Twig components.

Suppose you've already built a basic Twig component:

// src/Components/RandomNumberComponent.php
namespace App\Components;

use Symfony\UX\TwigComponent\Attribute\AsTwigComponent;

#[AsTwigComponent('random_number')]
class RandomNumberComponent
{
    public function getRandomNumber(): string
    {
        return rand(0, 1000);
    }
}

{# templates/components/random_number.html.twig #}
<div>
    <strong>{{ this.randomNumber }}</strong>
</div>

To transform this into a "live" component (i.e. one that can be re-rendered live on the frontend), replace the component's AsTwigComponent attribute with AsLiveComponent and add the DefaultActionTrait:

// src/Components/RandomNumberComponent.php

-use Symfony\UX\TwigComponent\Attribute\AsTwigComponent;
+use Symfony\UX\LiveComponent\Attribute\AsLiveComponent;
+use Symfony\UX\LiveComponent\DefaultActionTrait;

-#[AsTwigComponent('random_number')]
+#[AsLiveComponent('random_number')]
class RandomNumberComponent
{
+    use DefaultActionTrait;
}

Then, in the template, make sure there is one HTML element around your entire component and use the {{ init_live_component() }} function to initialize the Stimulus controller:

-<div>
+<div {{ init_live_component(this) }}>
    <strong>{{ this.randomNumber }}</strong>
</div>

Your component is now a live component... except that we haven't added anything that would cause the component to update. Let's start simple, by adding a button that - when clicked - will re-render the component and give the user a new random number:

<div {{ init_live_component(this) }}>
    <strong>{{ this.randomNumber }}</strong>

    <button
        data-action="live#$render"
    >Generate a new number!</button>
</div>

That's it! When you click the button, an Ajax call will be made to get a fresh copy of our component. That HTML will replace the current HTML. In other words, you just generated a new random number! That's cool, but let's keep going because... things get cooler.

LiveProps: Stateful Component Properties

Let's make our component more flexible by adding $min and $max properties:

// src/Components/RandomNumberComponent.php
namespace App\Components;

// ...
use Symfony\UX\LiveComponent\Attribute\LiveProp;

#[AsLiveComponent('random_number')]
class RandomNumberComponent
{
    #[LiveProp]
    public int $min = 0;

    #[LiveProp]
    public int $max = 1000;

    public function getRandomNumber(): string
    {
        return rand($this->min, $this->max);
    }

    // ...
}

With this change, we can control the $min and $max properties when rendering the component:

{{ component('random_number', { min: 5, max: 500 }) }}

But what's up with those LiveProp attributes? A property with the LiveProp attribute becomes a "stateful" property for this component. In other words, each time we click the "Generate a new number!" button, when the component re-renders, it will remember the original values for the $min and $max properties and generate a random number between 5 and 500. If you forgot to add LiveProp, when the component re-rendered, those two values would not be set on the object.

In short: LiveProps are "stateful properties": they will always be set when rendering. Most properties will be LiveProps, with common exceptions being properties that hold services (these don't need to be stateful because they will be autowired each time before the component is rendered) and properties used for computed properties.

data-action="live#update": Re-rendering on LiveProp Change

Could we allow the user to choose the $min and $max values and automatically re-render the component when they do? Definitely! And that is where live components really shine.

Let's add two inputs to our template:

{# templates/components/random_number.html.twig #}
<div {{ init_live_component(this) }}>
    <input
        type="number"
        value="{{ this.min }}"
        data-model="min"
        data-action="live#update"
    >

    <input
        type="number"
        value="{{ this.max }}"
        data-model="max"
        data-action="live#update"
    >

    Generating a number between {{ this.min }} and {{ this.max }}
    <strong>{{ this.randomNumber }}</strong>
</div>

Notice the data-action="live#update" on each input. When the user types, live components reads the data-model attribute (e.g. min) and re-renders the component using the new value for that field! Yes, as you type in a box, the component automatically updates to reflect the new number!

Well, actually, we're missing one step. By default, a LiveProp is "read only". For security purposes, a user cannot change the value of a LiveProp and re-render the component unless you allow it with the writable=true option:

// src/Components/RandomNumberComponent.php
// ...

class RandomNumberComponent
{
-    #[LiveProp]
+    #[LiveProp(writable: true)]
    public int $min = 0;

-   #[LiveProp]
+   #[LiveProp(writable: true)]
    public int $max = 1000;

    // ...
}

Now it works: as you type into the min or max boxes, the component will re-render with a new random number between that range!

Debouncing

If the user types 5 characters really quickly into an input, we don't want to send 5 Ajax requests. Fortunately, the live#update method has built-in debouncing: it waits for a 150ms pause before sending an Ajax request to re-render. This is built in, so you don't need to think about it.

Lazy Updating on "blur" or "change" of a Field

Sometimes, you might want a field to re-render only after the user has changed an input and moved to another field. Browsers dispatch a change event in this situation. To re-render when this event happens, add it to the data-action call:

<input
    type="number"
    value="{{ this.max }}"
    data-model="max"
-    data-action="live#update"
+    data-action="change->live#update"
>

The data-action="change->live#update" syntax is standard Stimulus syntax, which says:

When the "change" event occurs, call the update method on the live controller.

Deferring a Re-Render Until Later

Other times, you might want to update the internal value of a property, but wait until later to re-render the component (e.g. until a button is clicked). To do that, use the updateDefer method:

<input
    type="number"
    value="{{ this.max }}"
    data-model="max"
-    data-action="live#update"
+    data-action="live#updateDefer"
>

Now, as you type, the max "model" will be updated in JavaScript, but it won't, yet, make an Ajax call to re-render the component. Whenever the next re-render does happen, the updated max value will be used.

Using name="" instead of data-model

Instead of communicating the property name of a field via data-model, you can communicate it via the standard name property. The following code works identically to the previous example:

<div {{ init_live_component(this)>
    <input
        type="number"
        value="{{ this.min }}"
-        data-model="min"
+        name="min"
        data-action="live#update"
    >

    // ...
</div>

If an element has both data-model and name attributes, the data-model attribute takes precedence.

Loading States

Often, you'll want to show (or hide) an element while a component is re-rendering or an action is processing. For example:

<!-- show only when the component is loading -->
<span data-loading>Loading</span>

<!-- equalivalent, longer syntax -->
<span data-loading="show">Loading</span>

Or, to hide an element while the component is loading:

<!-- hide when the component is loading -->
<span
    data-loading="hide"
>Saved!</span>

Adding and Removing Classes or Attributes

Instead of hiding or showing an entire element, you could add or remove a class:

<!-- add this class when loading -->
<div data-loading="addClass(opacity-50)">...</div>

<!-- remove this class when loading -->
<div data-loading="removeClass(opacity-50)">...</div>

<!-- add multiple classes when loading -->
<div data-loading="addClass(opacity-50 disabled)">...</div>

Sometimes you may want to add or remove an attribute when loading. That can be accomplished with addAttribute or removeAttribute:

<!-- add the "disabled" attribute when loading -->
<div data-loading="addAttribute(disabled)">...</div>

You can also combine any number of directives by separating them with a space:

<div data-loading="addClass(opacity-50) addAttribute(disabled)">...</div>

Finally, you can add the delay modifier to not trigger the loading changes until loading has taken longer than a certain amount of time:

<!-- Add class after 200ms of loading -->
<div data-loading="delay|addClass(opacity-50)">...</div>

<!-- Show after 200ms of loading -->
<div data-loading="delay|show">Loading</div>

<!-- Show after 500ms of loading -->
<div data-loading="delay(500)|show">Loading</div>

Actions

Live components require a single "default action" that is used to re-render it. By default, this is an empty __invoke() method and can be added with the DefaultActionTrait. Live components are actually Symfony controllers so you can add the normal controller attributes/annotations (ie @Cache/@Security) to either the entire class just a single action.

You can also trigger custom actions on your component. Let's pretend we want to add a "Reset Min/Max" button to our "random number" component that, when clicked, sets the min/max numbers back to a default value.

First, add a method with a LiveAction attribute above it that does the work:

// src/Components/RandomNumberComponent.php
namespace App\Components;

// ...
use Symfony\UX\LiveComponent\Attribute\LiveAction;

class RandomNumberComponent
{
    // ...

    #[LiveAction]
    public function resetMinMax()
    {
        $this->min = 0;
        $this->max = 1000;
    }

    // ...
}

To call this, add data-action="live#action" and data-action-name to an element (e.g. a button or form):

<button
    data-action="live#action"
    data-action-name="resetMinMax"
>Reset Min/Max</button>

Done! When the user clicks this button, a POST request will be sent that will trigger the resetMinMax() method! After calling that method, the component will re-render like normal, using the new $min and $max properties!

You can also add several "modifiers" to the action:

<form>
    <button
        data-action="live#action"
        data-action-name="prevent|debounce(300)|save"
    >Save</button>
</form>

The prevent modifier would prevent the form from submitting (event.preventDefault()). The debounce(300) modifier will add 300ms of "debouncing" before the action is executed. In other words, if you click really fast 5 times, only one Ajax request will be made!

Actions & Services

One really neat thing about component actions is that they are real Symfony controllers. Internally, they are processed identically to a normal controller method that you would create with a route.

This means that, for example, you can use action autowiring:

// src/Components/RandomNumberComponent.php
namespace App\Components;

// ...
use Psr\Log\LoggerInterface;

class RandomNumberComponent
{
    // ...

    #[LiveAction]
    public function resetMinMax(LoggerInterface $logger)
    {
        $this->min = 0;
        $this->max = 1000;
        $logger->debug('The min/max were reset!');
    }

    // ...
}

Actions and CSRF Protection

When you trigger an action, a POST request is sent that contains a X-CSRF-TOKEN header. This header is automatically populated and validated. In other words... you get CSRF protection without any work.

Your only job is to make sure that the CSRF component is installed:

composer require symfony/security-csrf

Actions, Redirecting and AbstractController

Sometimes, you may want to redirect after an action is executed (e.g. your action saves a form and then you want to redirect to another page). You can do that by returning a RedirectResponse from your action:

// src/Components/RandomNumberComponent.php
namespace App\Components;

// ...
use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;

class RandomNumberComponent extends AbstractController
{
    // ...

    #[LiveAction]
    public function resetMinMax()
    {
        // ...

        $this->addFlash('success', 'Min/Max have been reset!');

        return $this->redirectToRoute('app_random_number');
    }

    // ...
}

You probably noticed one interesting trick: to make redirecting easier, the component now extends AbstractController! That is totally allowed, and gives you access to all of your normal controller shortcuts. We even added a flash message!

Forms

A component can also help render a Symfony form, either the entire form (useful for automatic validation as you type) or just one or some fields (e.g. a markdown preview for a textarea or dependent form fields).

Rendering an Entire Form in a Component

Suppose you have a PostType form class that's bound to a Post entity and you'd like to render this in a component so that you can get instant validation as the user types:

namespace App\Form;

use App\Entity\Post;
use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\OptionsResolver\OptionsResolver;

class PostType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('title')
            ->add('slug')
            ->add('content')
        ;
    }

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

Before you start thinking about the component, make sure that you have your controller set up so you can handle the form submit. There's nothing special about this controller: it's written however you normally write your form controller logic:

namespace App\Controller;

use App\Entity\Post;
use App\Form\PostType;
use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\Routing\Annotation\Route;

class PostController extends AbstractController
{
    /**
     * @Route("/admin/post/{id}/edit", name="app_post_edit")
     */
    public function edit(Request $request, Post $post): Response
    {
        $form = $this->createForm(PostType::class, $post);
        $form->handleRequest($request);

        if ($form->isSubmitted() && $form->isValid()) {
            $this->getDoctrine()->getManager()->flush();

            return $this->redirectToRoute('app_post_index');
        }

        // renderForm() is new in Symfony 5.3.
        // Use render() and call $form->createView() if on a lower version
        return $this->renderForm('post/edit.html.twig', [
            'post' => $post,
            'form' => $form,
        ]);
    }
}

Great! In the template, instead of rendering the form, let's render a post_form component that we will create next:

{# templates/post/edit.html.twig #}

{% extends 'base.html.twig' %}

{% block body %}
    <h1>Edit Post</h1>

    {{ component('post_form', {
        post: post,
        form: form
    }) }}
{% endblock %}

Ok: time to build that post_form component! The Live Components package comes with a special trait - ComponentWithFormTrait - to make it easy to deal with forms:

namespace App\Twig\Components;

use App\Entity\Post;
use App\Form\PostType;
use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
use Symfony\Component\Form\FormInterface;
use Symfony\UX\LiveComponent\Attribute\AsLiveComponent;
use Symfony\UX\LiveComponent\Attribute\LiveProp;
use Symfony\UX\LiveComponent\ComponentWithFormTrait;

#[AsLiveComponent('post_form')]
class PostFormComponent extends AbstractController
{
    use ComponentWithFormTrait;

    /**
     * The initial data used to create the form.
     *
     * Needed so the same form can be re-created
     * when the component is re-rendered via Ajax.
     *
     * The `fieldName` option is needed in this situation because
     * the form renders fields with names like `name="post[title]"`.
     * We set `fieldName: ''` so that this live prop doesn't collide
     * with that data. The value - initialFormData - could be anything.
     */
    #[LiveProp(fieldName: 'initialFormData')]
    public ?Post $post = null;

    /**
     * Used to re-create the PostType form for re-rendering.
     */
    protected function instantiateForm(): FormInterface
    {
        // we can extend AbstractController to get the normal shortcuts
        return $this->createForm(PostType::class, $this->post);
    }
}

The trait forces you to create an instantiateForm() method, which is used when the component is rendered via AJAX. Notice that, in order to recreate the same form, we pass in the Post object and set it as a LiveProp.

The template for this component will render the form, which is available as this.form thanks to the trait:

{# templates/components/post_form.html.twig #}
<div
    {{ init_live_component(this) }}
    {#
        Automatically catch all "change" events from the fields
        below and re-render the component.

        Another common value is "input", which renders whenever
        the "input" event fires (e.g. as you type in a field).
        Note: if you use "input", Symfony's form system trims empty
        spaces. This means that if the user types a space, then waits,
        the re-render will remove the space. Set the "trim" option
        to false on any fields with this problem.
    #}
    data-action="change->live#update"
>
    {{ form_start(this.form) }}
        {{ form_row(this.form.title) }}
        {{ form_row(this.form.slug) }}
        {{ form_row(this.form.content) }}

        <button>Save</button>
    {{ form_end(this.form) }}
</div>

Mostly, this is a pretty boring template! It includes the normal init_live_component(this) and then you render the form however you want.

But the result is incredible! As you finish changing each field, the component automatically re-renders - including showing any validation errors for that field! Amazing!

This is possible thanks to a few interesting pieces:

• data-action="change->live#update": instead of adding data-action to every field, you can place this on a parent element. Thanks to this, as you change or type into fields (i.e. the input event), the model for that field will update and the component will re-render.

• The fields in our form do not have a data-model="" attribute. But that's ok! When that is absent, the name attribute is used instead. ComponentWithFormTrait has a modifiable LiveProp that captures these and submits the form using them. That's right: each render time the component re-renders, the form is submitted using the values. However, if a field has not been modified yet by the user, its validation errors are cleared so that they aren't rendered.

Handling "Cannot dehydrate an unpersisted entity" Errors.

If you're building a form to create a new entity, then when you render the component, you may be passing in a new, non-persisted entity.

For example, imagine you create a new Post() in your controller, pass this "not-yet-persisted" entity into your template as a post variable and pass that into your component:

{{ component('post_form', {
    post: post,
    form: form
}) }}

If you do this, you'll likely see this error:

Cannot dehydrate an unpersisted entity (App\Entity\Post). If you want to allow this, add a dehydrateWith= option to LiveProp

The problem is that the Live component system doesn't know how to transform this object into something that can be sent to the frontend, called "dehydration". If an entity has already been saved to the database, its "id" is sent to the frontend. But if the entity hasn't been saved yet, that's not possible.

The solution is to pass null into your component instead of a non-persisted entity object. If you need to, you can re-create your new Post() inside of your component:

{{ component('post_form', {
-    post: post,
+    post: post.id ? post : null,
    form: form
}) }}

Form Rendering Problems

For the most part, rendering a form inside a component works beautifully. But there are a few situations when your form may not behave how you want.

A) Text Boxes Removing Trailing Spaces

If you're re-rendering a field on the input event (that's the default event on a field, which is fired each time you type in a text box), then if you type a "space" and pause for a moment, the space will disappear!

This is because Symfony text fields "trim spaces" automatically. When your component re-renders, the space will disappear... as the user is typing! To fix this, either re-render on the change event (which fires after the text box loses focus) or set the trim option of your field to false:

public function buildForm(FormBuilderInterface $builder, array $options)
{
    $builder
        // ...
        ->add('content', TextareaType::class, [
            'trim' => false,
        ])
    ;
}

B) PasswordType loses the password on re-render

If you're using the PasswordType, when the component re-renders, the input will become blank! That's because, by default, the PasswordType does not re-fill the <input type="password"> after a submit.

To fix this, set the always_empty option to false in your form:

public function buildForm(FormBuilderInterface $builder, array $options)
{
    $builder
        // ...
        ->add('plainPassword', PasswordType::class, [
            'always_empty' => false,
        ])
    ;
}

Submitting the Form via an action()

Notice that, while we could add a save() component action that handles the form submit through the component, we've chosen not to do that so far. The reason is simple: by creating a normal route & controller that handles the submit, our form continues to work without JavaScript.

However, you can do this if you'd like. In that case, you wouldn't need any form logic in your controller:

/**
 * @Route("/admin/post/{id}/edit", name="app_post_edit")
 */
public function edit(Post $post): Response
{
    return $this->render('post/edit.html.twig', [
        'post' => $post,
    ]);
}

And you wouldn't pass any form into the component:

{# templates/post/edit.html.twig #}

<h1>Edit Post</h1>

{{ component('post_form', {
    post: post
}) }}

When you do not pass a form into a component that uses ComponentWithFormTrait, the form will be created for you automatically. Let's add the save() action to the component:

// ...
use Doctrine\ORM\EntityManagerInterface;
use Symfony\UX\LiveComponent\Attribute\LiveAction;

class PostFormComponent extends AbstractController
{
    // ...

    #[LiveAction]
    public function save(EntityManagerInterface $entityManager)
    {
        // shortcut to submit the form with form values
        // if any validation fails, an exception is thrown automatically
        // and the component will be re-rendered with the form errors
        $this->submitForm();

        /** @var Post $post */
        $post = $this->getFormInstance()->getData();
        $entityManager->persist($post);
        $entityManager->flush();

        $this->addFlash('success', 'Post saved!');

        return $this->redirectToRoute('app_post_show', [
            'id' => $this->post->getId(),
        ]);
    }
}

Finally, tell the form element to use this action:

{# templates/components/post_form.html.twig #}
{# ... #}

{{ form_start(this.form, {
    attr: {
        'data-action': 'live#action',
        'data-action-name': 'prevent|save'
    }
}) }}

Now, when the form is submitted, it will execute the save() method via Ajax. If the form fails validation, it will re-render with the errors. And if it's successful, it will redirect.

NOTE: Make sure that each time the user changes a field, you update the component's model. If you don't do this, when you trigger the action, it will not contain the form's data because the data in the fields and the component's data will be out of sync.

An easy way to accomplish this (explained more in the Forms section above) is to add:

<div
    {{ init_live_component(this) }}
+    data-action="change->live#update"
>

Modifying Embedded Properties with the "exposed" Option

If your component will render a form, you don't need to use the Symfony form component. Let's build an EditPostComponent without a form. This will need one LiveProp: the Post object that is being edited:

namespace App\Twig\Components;

use App\Entity\Post;
use Symfony\UX\LiveComponent\Attribute\AsLiveComponent;
use Symfony\UX\LiveComponent\Attribute\LiveProp;

#[AsLiveComponent('edit_post')]
class EditPostComponent
{
    #[LiveProp]
    public Post $post;
}

In the template, let's render an HTML form and a "preview" area where the user can see, as they type, what the post will look like (including rendered the content through a Markdown filter from the twig/markdown-extra library):

<div {{ init_live_component(this) }}>
    <input
        type="text"
        value="{{ this.post.title }}"
        data-model="post.title"
        data-action="live#update"
    >

    <textarea
        data-model="post.content"
        data-action="live#update"
    >{{ this.post.content }}</textarea>

    <div class="markdown-preview" data-loading="addClass(low-opacity)">
        <h3>{{ this.post.title }}</h3>
        {{ this.post.content|markdown_to_html }}
    </div>
</div>

This is pretty straightforward, except for one thing: the data-model attributes aren't targeting properties on the component class itself, they're targeting embedded properties within the $post property.

Out-of-the-box, modifying embedded properties is not allowed. However, you can enable it via the exposed option:

// ...

class EditPostComponent
{
-   #[LiveProp]
+   #[LiveProp(exposed: ['title', 'content'])]
    public Post $post;

    // ...
}

With this, both the title and the content properties of the $post property can be modified by the user. However, notice that the LiveProp does not have modifiable=true. This means that while the title and content properties can be changed, the Post object itself cannot be changed. In other words, if the component was originally created with a Post object with id=2, a bad user could not make a request that renders the component with id=3. Your component is protected from someone changing to see the form for a different Post object, unless you added writable=true to this property.

Validation (without a Form)

NOTE If your component contains a form, then validation is built-in automatically. Follow those docs for more details.

If you're building some sort of form without using Symfony's form component, you can still validate your data.

First use the ValidatableComponentTrait and add any constraints you need:

use App\Entity\User;
use Symfony\UX\LiveComponent\Attribute\AsLiveComponent;
use Symfony\UX\LiveComponent\Attribute\LiveProp;
use Symfony\UX\LiveComponent\ValidatableComponentTrait;
use Symfony\Component\Validator\Constraints as Assert;

#[AsLiveComponent('edit_user')]
class EditUserComponent
{
    use ValidatableComponentTrait;

    #[LiveProp(exposed: ['email', 'plainPassword'])]
    #[Assert\Valid]
    public User $user;

     #[LiveProp]
     #[Assert\IsTrue]
    public bool $agreeToTerms = false;
}

Be sure to add the IsValid attribute/annotation to any property where you want the object on that property to also be validated.

Thanks to this setup, the component will now be automatically validated on each render, but in a smart way: a property will only be validated once its "model" has been updated on the frontend. The system keeps track of which models have been updated (e.g. data-action="live#update") and only stores the errors for those fields on re-render.

You can also trigger validation of your entire object manually in an action:

use Symfony\UX\LiveComponent\Attribute\LiveAction;

#[AsLiveComponent('edit_user')]
class EditUserComponent
{
    // ...

    #[LiveAction]
    public function save()
    {
        // this will throw an exception if validation fails
        $this->validate();

        // perform save operations
    }
}

If validation fails, an exception is thrown, but the component will be re-rendered. In your template, render errors using the getError() method:

{% if this.getError('post.content') %}
    <div class="error">
        {{ this.getError('post.content').message }}
    </div>
{% endif %}
<textarea
    data-model="post.content"
    data-action="live#update"
    class="{{ this.getError('post.content') ? 'has-error' : '' }}"
>{{ this.post.content }}</textarea>

Once a component has been validated, the component will "rememeber" that it has been validated. This means that, if you edit a field and the component re-renders, it will be validated again.

Real Time Validation

As soon as you enable validation, each field will automatically be validated when its model is updated. For example, if you want a single field to be validated "on change" (when you change the field and then blur the field), update the model via the change event:

<textarea
    data-model="post.content"
    data-action="change->live#update"
    class="{{ this.getError('post.content') ? 'has-error' : '' }}"
>{{ this.post.content }}</textarea>

When the component re-renders, it will signal to the server that this one field should be validated. Like with normal validation, once an individual field has been validated, the component "remembers" that, and re-validates it on each render.

Polling

You can also use "polling" to continually refresh a component. On the top-level element for your component, add data-poll:

<div
    {{ init_live_component(this) }}
+    data-poll
>

This will make a request every 2 seconds to re-render the component. You can change this by adding a delay() modifier. When you do this, you need to be specific that you want to call the $render method. To delay for 500ms:

<div
    {{ init_live_component(this) }}
    data-poll="delay(500)|$render"
>

You can also trigger a specific "action" instead of a normal re-render:

<div
    {{ init_live_component(this) }}

    data-poll="save"
    {#
    Or add a delay() modifier:
    data-poll="delay(2000)|save"
    #}
>

Embedded Components

Need to embed one live component inside another one? No problem! As a rule of thumb, each component exists in its own, isolated universe. This means that embedding one component inside another could be really simple or a bit more complex, depending on how inter-connected you want your components to be.

Here are a few helpful things to know:

Each component re-renders independent of one another

If a parent component re-renders, the child component will not (most of the time) be updated, even though it lives inside the parent. Each component is its own, isolated universe.

But this is not always what you want. For example, suppose you have a parent component that renders a form and a child component that renders one field in that form. When you click a "Save" button on the parent component, that validates the form and re-renders with errors - including a new error value that it passes into the child:

{# templates/components/post_form.html.twig #}

{{ component('textarea_field', {
    value: this.content,
    error: this.getError('content')
}) }}

In this situation, when the parent component re-renders after clicking "Save", you do want the updated child component (with the validation error) to be rendered. And this will happen automatically. Why? because the live component system detects that the parent component has changed how it's rendering the child.

This may not always be perfect, and if your child component has its own LiveProp that has changed since it was first rendered, that value will be lost when the parent component causes the child to re-render. If you have this situation, use data-model-map to map that child LiveProp to a LiveProp in the parent component, and pass it into the child when rendering.

Actions, methods and model updates in a child do not affect the parent

Again, each component is its own, isolated universe! For example, suppose your child component has:

<button data-action="live#action" data-action-name="save">Save</button>

When the user clicks that button, it will attempt to call the save action in the child component only, even if the save action actually only exists in the parent. The same is true for data-model, though there is some special handling for this case (see next point).

If a child model updates, it will attempt to update the parent model

Suppose a child component has a:

<textarea data-model="markdown_value" data-action="live#update">

When the user changes this field, this will only update the markdown_value field in the child component... because (yup, we're saying it again): each component is its own, isolated universe.

However, sometimes this isn't what you want! Sometimes, in addition to updating the child component's model, you also want to update a model on the parent component.

To help with this, whenever a model updates, a live:update-model event is dispatched. All components automatically listen to this event. This means that, when the markdown_value model is updated in the child component, if the parent component also has a model called markdown_value it will also be updated. This is done as a "deferred" update (i.e. updateDefer()).

If the model name in your child component (e.g. markdown_value) is different than the model name in your parent component (e.g. post.content), you have two options. First, you can make sure both are set by leveraging both the data-model and name attributes:

<textarea
    data-model="markdown_value"
    name="post[content]"
    data-action="live#update"
>

In this situation, the markdown_value model will be updated on the child component (because data-model takes precedence over name). But if any parent components have a markdown_value model or a post.content model (normalized from post[content]`), their model will also be updated.

A second option is to wrap your child element in a special data-model-map element:

{# templates/components/post_form.html.twig #}

<div data-model-map="from(markdown_value)|post.content">
    {{ component('textarea_field', {
        value: this.content,
        error: this.getError('content')
    }) }}
</div>

Thanks to the data-model-map, whenever the markdown_value model updates in the child component, the post.content model will be updated in the parent component.

NOTE: If you change a LiveProp of a child component on the server (e.g. during re-rendering or via an action), that change will not be reflected on any parent components that share that model.

Full Embedded Component Example

Let's look at a full, complex example of an embedded component. Suppose you have an EditPostComponent:

<?php

namespace App\Twig\Components;

use App\Entity\Post;
use Doctrine\ORM\EntityManagerInterface;
use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
use Symfony\UX\LiveComponent\Attribute\AsLiveComponent;
use Symfony\UX\LiveComponent\Attribute\LiveAction;
use Symfony\UX\LiveComponent\Attribute\LiveProp;

#[AsLiveComponent('edit_post')]
final class EditPostComponent extends AbstractController
{
    #[LiveProp(exposed: ['title', 'content'])]
    public Post $post;

    #[LiveAction]
    public function save(EntityManagerInterface $entityManager)
    {
        $entityManager->flush();

        return $this->redirectToRoute('some_route');
    }
}

And a MarkdownTextareaComponent:

<?php

namespace App\Twig\Components;

use Symfony\UX\LiveComponent\Attribute\AsLiveComponent;
use Symfony\UX\LiveComponent\Attribute\LiveProp;

#[AsLiveComponent('markdown_textarea')]
final class MarkdownTextareaComponent
{
    #[LiveProp]
    public string $label;

    #[LiveProp]
    public string $name;

    #[LiveProp(writable: true)]
    public string $value = '';
}

In the EditPostComponent template, you render the MarkdownTextareaComponent:

{# templates/components/edit_post.html.twig #}
<div {{ init_live_component(this) }}>
    <input
        type="text"
        name="post[title]"
        data-action="live#update"
        value="{{ this.post.title }}"
    >

    {{ component('markdown_textarea', {
        name: 'post[content]',
        label: 'Content',
        value: this.post.content
    }) }}

    <button
        data-action="live#action"
        data-action-name="save"
    >Save</button>
</div>

<div {{ init_live_component(this) }} class="mb-3">
    <textarea
        name="{{ this.name }}"
        data-model="value"
        data-action="live#update"
    >{{ this.value }}</textarea>

    <div class="markdown-preview">
        {{ this.value|markdown_to_html }}
    </div>
</div>

Notice that MarkdownTextareaComponent allows a dynamic name attribute to be passed in. This makes that component re-usable in any form. But it also makes sure that when the textarea changes, both the value model in MarkdownTextareaComponent and the post.content model in EditPostcomponent will be updated.