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How to Create and Use Workflows

4.2 version
Maintained Unmaintained

How to Create and Use Workflows

Installation

In applications using Symfony Flex, run this command to install the workflow feature before using it:

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$ composer require symfony/workflow

Creating a Workflow

A workflow is a process or a lifecycle that your objects go through. Each step or stage in the process is called a place. You do also define transitions to that describes the action to get from one place to another.

../_images/states_transitions.png

A set of places and transitions creates a definition. A workflow needs a Definition and a way to write the states to the objects (i.e. an instance of a MarkingStoreInterface.)

Consider the following example for a blog post that can have these places: draft, review, rejected, published. You can define the workflow like this:

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    # config/packages/workflow.yaml
    framework:
        workflows:
            blog_publishing:
                type: 'workflow' # or 'state_machine'
                marking_store:
                    type: 'multiple_state' # or 'single_state'
                    arguments:
                        - 'currentPlace'
                supports:
                    - App\Entity\BlogPost
                initial_place: draft
                places:
                    - draft
                    - review
                    - rejected
                    - published
                transitions:
                    to_review:
                        from: draft
                        to:   review
                    publish:
                        from: review
                        to:   published
                    reject:
                        from: review
                        to:   rejected
    
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    <!-- config/packages/workflow.xml -->
    <?xml version="1.0" encoding="utf-8" ?>
    <container xmlns="http://symfony.com/schema/dic/services"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xmlns:framework="http://symfony.com/schema/dic/symfony"
        xsi:schemaLocation="http://symfony.com/schema/dic/services http://symfony.com/schema/dic/services/services-1.0.xsd
            http://symfony.com/schema/dic/symfony http://symfony.com/schema/dic/symfony/symfony-1.0.xsd"
    >
    
        <framework:config>
            <framework:workflow name="blog_publishing" type="workflow">
                <framework:marking-store type="single_state">
                  <framework:argument>currentPlace</framework:argument>
                </framework:marking-store>
    
                <framework:support>App\Entity\BlogPost</framework:support>
    
                <framework:place>draft</framework:place>
                <framework:place>review</framework:place>
                <framework:place>rejected</framework:place>
                <framework:place>published</framework:place>
    
                <framework:transition name="to_review">
                    <framework:from>draft</framework:from>
    
                    <framework:to>review</framework:to>
                </framework:transition>
    
                <framework:transition name="publish">
                    <framework:from>review</framework:from>
    
                    <framework:to>published</framework:to>
                </framework:transition>
    
                <framework:transition name="reject">
                    <framework:from>review</framework:from>
    
                    <framework:to>rejected</framework:to>
                </framework:transition>
    
            </framework:workflow>
    
        </framework:config>
    </container>
    
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    // config/packages/workflow.php
    
    $container->loadFromExtension('framework', array(
        // ...
        'workflows' => array(
            'blog_publishing' => array(
                'type' => 'workflow', // or 'state_machine'
                'marking_store' => array(
                    'type' => 'multiple_state', // or 'single_state'
                    'arguments' => array('currentPlace')
                ),
                'supports' => array('App\Entity\BlogPost'),
                'places' => array(
                    'draft',
                    'review',
                    'rejected',
                    'published',
                ),
                'transitions' => array(
                    'to_review' => array(
                        'from' => 'draft',
                        'to' => 'review',
                     ),
                     'publish' => array(
                         'from' => 'review',
                         'to' => 'published',
                     ),
                     'reject' => array(
                         'from' => 'review',
                         'to' => 'rejected',
                     ),
                 ),
             ),
         ),
     ));
    
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class BlogPost
{
    // This property is used by the marking store
    public $currentPlace;
    public $title;
    public $content;
}

Note

The marking store type could be "multiple_state" or "single_state". A single state marking store does not support a model being on multiple places at the same time.

Tip

The type (default value single_state) and arguments (default value marking) attributes of the marking_store option are optional. If omitted, their default values will be used.

Using a Workflow

Once the blog_publishing workflow has been created, you can now use it to decide what actions are allowed on a blog post. For example, inside a controller of an application using the default services.yaml configuration, you can get the workflow by injecting the Workflow registry service:

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// ...
use Symfony\Component\Workflow\Registry;
use App\Entity\BlogPost;
use Symfony\Bundle\FrameworkBundle\Controller\Controller;
use Symfony\Component\Workflow\Exception\TransitionException;

class BlogController extends Controller
{
    public function edit(Registry $workflows)
    {
        $post = new BlogPost();
        $workflow = $workflows->get($post);

        // if there are multiple workflows for the same class,
        // pass the workflow name as the second argument
        // $workflow = $workflows->get($post, 'blog_publishing');

        // you can also get all workflows associated with an object, which is useful
        // for example to show the status of all those workflows in a backend
        $postWorkflows = $workflows->all($post);

        $workflow->can($post, 'publish'); // False
        $workflow->can($post, 'to_review'); // True

        // Update the currentState on the post
        try {
            $workflow->apply($post, 'to_review');
        } catch (TransitionException $exception) {
            // ... if the transition is not allowed
        }

        // See all the available transitions for the post in the current state
        $transitions = $workflow->getEnabledTransitions($post);
    }
}

New in version 4.1: The TransitionException class was introduced in Symfony 4.1.

New in version 4.1: The all() method was introduced in Symfony 4.1.

Using Events

To make your workflows more flexible, you can construct the Workflow object with an EventDispatcher. You can now create event listeners to block transitions (i.e. depending on the data in the blog post) and do additional actions when a workflow operation happened (e.g. sending announcements).

Each step has three events that are fired in order:

  • An event for every workflow;
  • An event for the workflow concerned;
  • An event for the workflow concerned with the specific transition or place name.

When a state transition is initiated, the events are dispatched in the following order:

workflow.guard

Validate whether the transition is allowed at all (see below).

The three events being dispatched are:

  • workflow.guard
  • workflow.[workflow name].guard
  • workflow.[workflow name].guard.[transition name]
workflow.leave

The subject is about to leave a place.

The three events being dispatched are:

  • workflow.leave
  • workflow.[workflow name].leave
  • workflow.[workflow name].leave.[place name]
workflow.transition

The subject is going through this transition.

The three events being dispatched are:

  • workflow.transition
  • workflow.[workflow name].transition
  • workflow.[workflow name].transition.[transition name]
workflow.enter

The subject is about to enter a new place. This event is triggered just before the subject places are updated, which means that the marking of the subject is not yet updated with the new places.

The three events being dispatched are:

  • workflow.enter
  • workflow.[workflow name].enter
  • workflow.[workflow name].enter.[place name]
workflow.entered

The subject has entered in the places and the marking is updated (making it a good place to flush data in Doctrine).

The three events being dispatched are:

  • workflow.entered
  • workflow.[workflow name].entered
  • workflow.[workflow name].entered.[place name]
workflow.completed

The object has completed this transition.

The three events being dispatched are:

  • workflow.completed
  • workflow.[workflow name].completed
  • workflow.[workflow name].completed.[transition name]
workflow.announce

Triggered for each transition that now is accessible for the subject.

The three events being dispatched are:

  • workflow.announce
  • workflow.[workflow name].announce
  • workflow.[workflow name].announce.[transition name]

Note

The leaving and entering events are triggered even for transitions that stay in same place.

Here is an example of how to enable logging for every time the blog_publishing workflow leaves a place:

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use Psr\Log\LoggerInterface;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\Workflow\Event\Event;

class WorkflowLogger implements EventSubscriberInterface
{
    public function __construct(LoggerInterface $logger)
    {
        $this->logger = $logger;
    }

    public function onLeave(Event $event)
    {
        $this->logger->alert(sprintf(
            'Blog post (id: "%s") performed transaction "%s" from "%s" to "%s"',
            $event->getSubject()->getId(),
            $event->getTransition()->getName(),
            implode(', ', array_keys($event->getMarking()->getPlaces())),
            implode(', ', $event->getTransition()->getTos())
        ));
    }

    public static function getSubscribedEvents()
    {
        return array(
            'workflow.blog_publishing.leave' => 'onLeave',
        );
    }
}

Guard Events

There are a special kind of events called "Guard events". Their event listeners are invoked every time a call to Workflow::can, Workflow::apply or Workflow::getEnabledTransitions is executed. With the guard events you may add custom logic to decide what transitions that are valid or not. Here is a list of the guard event names.

  • workflow.guard
  • workflow.[workflow name].guard
  • workflow.[workflow name].guard.[transition name]

See example to make sure no blog post without title is moved to "review":

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use Symfony\Component\Workflow\Event\GuardEvent;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;

class BlogPostReviewListener implements EventSubscriberInterface
{
    public function guardReview(GuardEvent $event)
    {
        /** @var \App\Entity\BlogPost $post */
        $post = $event->getSubject();
        $title = $post->title;

        if (empty($title)) {
            // Posts with no title should not be allowed
            $event->setBlocked(true);
        }
    }

    public static function getSubscribedEvents()
    {
        return array(
            'workflow.blogpost.guard.to_review' => array('guardReview'),
        );
    }
}

Event Methods

Each workflow event is an instance of Event. This means that each event has access to the following information:

getMarking()
Returns the Marking of the workflow.
getSubject()
Returns the object that dispatches the event.
getTransition()
Returns the Transition that dispatches the event.
getWorkflowName()
Returns a string with the name of the workflow that triggered the event.

For Guard Events, there is an extended class GuardEvent. This class has two more methods:

isBlocked()
Returns if transition is blocked.
setBlocked()
Sets the blocked value.

Usage in Twig

Symfony defines several Twig functions to manage workflows and reduce the need of domain logic in your templates:

workflow_can()
Returns true if the given object can make the given transition.
workflow_transitions()
Returns an array with all the transitions enabled for the given object.
workflow_marked_places()
Returns an array with the place names of the given marking.
workflow_has_marked_place()
Returns true if the marking of the given object has the given state.

The following example shows these functions in action:

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<h3>Actions</h3>
{% if workflow_can(post, 'publish') %}
    <a href="...">Publish article</a>
{% endif %}
{% if workflow_can(post, 'to_review') %}
    <a href="...">Submit to review</a>
{% endif %}
{% if workflow_can(post, 'reject') %}
    <a href="...">Reject article</a>
{% endif %}

{# Or loop through the enabled transitions #}
{% for transition in workflow_transitions(post) %}
    <a href="...">{{ transition.name }}</a>
{% else %}
    No actions available.
{% endfor %}

{# Check if the object is in some specific place #}
{% if workflow_has_marked_place(post, 'to_review') %}
    <p>This post is ready for review.</p>
{% endif %}

{# Check if some place has been marked on the object #}
{% if 'waiting_some_approval' in workflow_marked_places(post) %}
    <span class="label">PENDING</span>
{% endif %}

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