PHP workflows – ezComponents

Workflows are a useful tool to help manage business processes. In this post I take a look at the workflow engine of eZ components, which was developed by Sebastian Bergmann. In this post, I introduce the basics of the workflow engine, and will expand on it’s usage in future posts.

The first step is to download eZ components. At time of writing, the latest version is 2009.1.1 – eZ components can be downloaded from: http://www.ezcomponents.org/download

$ mkdir workflow
$ cd workflow/
$ wget http://www.ezcomponents.org/files/downloads/ezcomponents-2009.1.1.tar.bz2
$ tar -xjf
$ tar -xjf ezcomponents-2009.1.1.tar.bz2
$ cd ezcomponents-2009.1.1

A workflow flows from node to node, sometimes branching conditionally, or splitting to parallel tasks. It flows from the startNode, to the endNode, unless the process is canceled at some point during execution. We start with a really basic workflow, which when started will simply write ‘Hello world’ to the screen.

 'myServiceObject'));

$workflow->startNode->addoutNode($step1);
$step1->addOutNode($workflow->endNode);

$execution = new ezcWorkflowExecutionNonInteractive();
$execution->workflow = $workflow;
$execution->start();

if ($execution->hasEnded())
  echo "Execution has ended.n";
else
  echo "Execution has NOT ended?n";

lines 1-8

These lines just setup the autoloader

line 10

Creates a workflow with a name ‘Example 1’

lines 12-23

The ezcWorkflowServiceObject interface can be implemented to provide custom code that can be executed by a ezcWorkflowNodeAction once it is reached in the workflow. If execute() returns true, the workflow proceeds, else it is stalled.

line 25

Creates a action node, which will instance and execute the myServiceObject class when reached.

line 27-28

Defines step1 as the action node, linking it to the outNode of the workflows start, and linking it’s own outNode to the endNode of the workflow.

line 30-32

An execution object is created, the workflow assigned, and the execution is started.

line 34-38

Checks that the workflow is complete as we’d expect it to be

The output of this script is as follows:

$ php ./eg1.php
Hello world!
Execution has ended.

We will now modify this example to be a little more personal. We will introduce an input node, which will stall the workflow execution until required input is acquired, and provided to the workflow. Once the input is provided, execution continues to an action node which instances a slightly modified service object, which says hello.

# cat ./eg2.php
getVariable('name');
    echo "Hello {$name}!n";
  }

  public function __toString()
  {
    return __CLASS__;
  }
}

$getName = new ezcWorkflowNodeInput(array(
  'name' => new ezcWorkflowConditionIsString()
));

$sayHello = new ezcWorkflowNodeAction(array('class' => 'myServiceObject'));

$workflow->startNode->addoutNode($getName);
$getName->addOutNode($sayHello);
$sayHello->addoutNode($workflow->endNode);

$db = ezcDbFactory::create('sqlite://:memory:');
$schema = ezcDbSchema::createFromFile('array', './WorkflowDatabaseTiein/tests/workflow.dba');
$schema->writeToDb($db);

$execution = new ezcWorkflowDatabaseExecution($db);
$execution->workflow = $workflow;
$execution->start();

if ($execution->hasEnded())
  echo "Execution has ended.n";
else
  echo "Execution has NOT ended?n";

$execution->resume(array('name' => 'Fred'));

if ($execution->hasEnded())
  echo "Execution has ended.n";
else
  echo "Execution has NOT ended?n";

The code is very similar to the first example, so I’ll cover just the main differences below:

line 17

Accesses a variable called ‘name’ of the workflow

line 27-29

Creates an input node, which will take input from the application. In this instance it’s requiring a ‘name’ of type string.

line 33-35

Configuring the work flow

line 37-39

The details of this will be covered in my next post on the workflow component

Execution of the workflow is started in this example in much the same was as the previous example – however execution does not finish on the first call to $execution->start(). This is because of the input node requiring a ‘name’ before it can continue. In line 50, we ask the exeuction to resume, providing the name , at which point execution continues, prints hello, and then finishes. The output is as follows:

$ php ./eg2.php
Execution has NOT ended?
Hello Fred!
Execution has ended.

In a follow up post, I will show a more realistic use of workflows, and show a few more of the workflow components in action.