instance of a:class:`Symfony\\Component\\Workflow\\MarkingStore\\MarkingStoreInterface`.)

Consider the following example for a blog post that can have these places:

``draft``, ``review``, ``rejected``, ``published``. You can define the workflow

``draft``, ``reviewed``, ``rejected``, ``published``. You can define the workflow

like this:

..configuration-block::

..code-block::xml

order:

``workflow.guard``

Validate whether the transition isallowed at all (:ref:`see below<workflow-usage-guard-events>`).

Validate whether the transition isblocked or not (:ref:`see below<workflow-usage-guard-events>` and:ref:`using guards<workflow-usage-using-guards>`).

The three events being dispatched are:

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 transitionsare valid or not. Here is a list

add custom logic to decide what transitionsshould be blocked 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"::

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

:method:`Symfony\\Component\\Workflow\\Event\\GuardEvent::setBlocked`

Sets the blocked value.

.. _workflow-usage-using-guards:

Using Guards

The component has a guard logic to control the execution of your workflow on top of your configuration.

It allows you to execute your custom logic to decide if the transition is blocked or not, before actually

applying this transition.

You have multiple optional ways to use guards in your workflow.

The first way is:ref:`with the guard event<workflow-usage-guard-events>`, which allows you to implement

any desired feature.

Another one is via the configuration and its specific entry `guard` on a transition.

This `guard` entry allows any expression that is valid for the Expression Language component:

..configuration-block::

..code-block::yaml

Usage in Twig

{% endfor %}

{# Check if the object is in some specific place #}

{% if workflow_has_marked_place(post, 'review') %}

{% if workflow_has_marked_place(post, 'reviewed') %}

<p>This post is ready for review.</p>

{% endif %}