Mar 23, 2019 · Mar 23, 2019 · Mar 23, 2019
diff --git a/workflow/usage.rst b/workflow/usage.rst
    {% if 'waiting_some_approval' in workflow_marked_places(post) %}
        <span class="label">PENDING</span>
    {% endif %}

 Transition Blockers
 -------------------

 .. versionadded:: 4.1
    Transition Blockers were introduced in Symfony 4.1.

 Transition Blockers provide a simple way to return a human-readable message for why a transition
 was blocked. You can access the message from Twig. Here's an example:


 .. code-block:: php

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

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

            // If it's after 9pm, prevent publication
            if (date('H') > 21) {
                $event->addTransitionBlocker(
                    new TransitionBlocker(
                        "You can not publish this blog post because it's too late. Try again tomorrow morning."
                    )
                );
            }
        }

        public static function getSubscribedEvents()
        {
            return [
                'workflow.blogpost.guard.publish' => ['guardPublish'],
            ];
        }
    }

 .. code-block:: html+twig

    <h2>Publication was blocked because:</h2>
    <ul>
        {% for transition in workflow_all_transitions(article) %}
            {% if not workflow_can(article, transition.name) %}
                <li>
                    <strong>{{ transition.name }}</strong>:
                    <ul>
                    {% for blocker in workflow_build_transition_blocker_list(article, transition.name) %}
                        <li>
                            {{ blocker.message }}
                            {% if blocker.parameters.expression is defined %}
                                <code>{{ blocker.parameters.expression }}</code>
                            {% endif %}
                        </li>
                    {% endfor %}
                    </ul>
                </li>
            {% endif %}
        {% endfor %}
    </ul>

 Don't need a human-readable message? You can still use::

    $event->setBlocked('true');
Original file line number	Diff line number	Diff line change
Expand Up		@@ -475,3 +475,70 @@ The following example shows these functions in action:
		{% if 'waiting_some_approval' in workflow_marked_places(post) %}
		<span class="label">PENDING</span>
		{% endif %}

		Transition Blockers
		-------------------

		.. versionadded:: 4.1
		Transition Blockers were introduced in Symfony 4.1.

		Transition Blockers provide a simple way to return a human-readable message for why a transition
		was blocked. You can access the message from Twig. Here's an example:


		.. code-block:: php

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

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

		// If it's after 9pm, prevent publication
		if (date('H') > 21) {
		$event->addTransitionBlocker(
		new TransitionBlocker(
		"You can not publish this blog post because it's too late. Try again tomorrow morning."
		)
		);
		}
		}

		public static function getSubscribedEvents()
		{
		return [
		'workflow.blogpost.guard.publish' => ['guardPublish'],
		];
		}
		}

		.. code-block:: html+twig

		<h2>Publication was blocked because:</h2>
		<ul>
		{% for transition in workflow_all_transitions(article) %}
		{% if not workflow_can(article, transition.name) %}
		<li>
		<strong>{{ transition.name }}</strong>:
		<ul>
		{% for blocker in workflow_build_transition_blocker_list(article, transition.name) %}
		<li>
		{{ blocker.message }}
		{% if blocker.parameters.expression is defined %}
		<code>{{ blocker.parameters.expression }}</code>
		{% endif %}
		</li>
		{% endfor %}
		</ul>
		</li>
		{% endif %}
		{% endfor %}
		</ul>

		Don't need a human-readable message? You can still use::

		$event->setBlocked('true');