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The Workflow component provides tools for managing a workflow or finite state machine.

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$ composer require symfony/workflow

The workflow component gives you an object oriented way to define a process or a life cycle that your object goes through. Each step or stage in the process is called a place. You do also define transitions that describe the action to get from one place to another.

An example state diagram for a workflow, showing transitions and places.

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. A post can have one of a number of predefined statuses (draft, reviewed, rejected, published). In a workflow, these statuses are called places. You can define the workflow like this:

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use Symfony\Component\Workflow\DefinitionBuilder;
use Symfony\Component\Workflow\MarkingStore\MethodMarkingStore;
use Symfony\Component\Workflow\Transition;
use Symfony\Component\Workflow\Workflow;

$definitionBuilder = new DefinitionBuilder();
$definition = $definitionBuilder->addPlaces(['draft', 'reviewed', 'rejected', 'published'])
    // Transitions are defined with a unique name, an origin place and a destination place
    ->addTransition(new Transition('to_review', 'draft', 'reviewed'))
    ->addTransition(new Transition('publish', 'reviewed', 'published'))
    ->addTransition(new Transition('reject', 'reviewed', 'rejected'))
    ->build()
;

$singleState = true; // true if the subject can be in only one state at a given time
$property = 'currentState'; // subject property name where the state is stored
$marking = new MethodMarkingStore($singleState, $property);
$workflow = new Workflow($definition, $marking);

The Workflow can now help you to decide what transitions (actions) are allowed on a blog post depending on what place (state) it is in. This will keep your domain logic in one place and not spread all over your application.

Here's an example of using the workflow defined above:

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// ...
// Consider that $blogPost is in place "draft" by default
$blogPost = new BlogPost();

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

$workflow->apply($blogPost, 'to_review'); // $blogPost is now in place "reviewed"

$workflow->can($blogPost, 'publish'); // True
$workflow->getEnabledTransitions($blogPost); // $blogPost can perform transition "publish" or "reject"

If the marking property of your object is null and you want to set it with the initial_marking from the configuration, you can call the getMarking() method to initialize the object property:

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// ...
$blogPost = new BlogPost();

// initiate workflow
$workflow->getMarking($blogPost);

Read more about the usage of the Workflow component inside a Symfony application.

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