how to inject class dependency in Yii2 configuration? - dependency-injection

Question

I am learning Yii2. Here is one situation I have not googled the answer.
I register a component called scraper in config/console.php's $config['components'] array,
this scraper class has a public property $_client which is a Goutte\Client class.
I tried to use the following way to set up scraper component, but it is not working, Yii2 did not instantiate $_client as a Goutte\Client object.
$config = [
'scraper' => [
'class' => 'app\models\Scraper',
'_pageSize' => 10,
'_client' => [ //not working. can not instantiate this property as an object
'class' => 'Goutte\Client'
],
],
//...
]
Question: What would be working way to inject the dependency in the configuration?

Answer 1

Yii2 will not instantiate objects beyond the first level in your config array. In other words, scraper will get instantiated as an object, but it's property _client will be instantiated as an array ['class' => 'Goutte\Client'].
You should implement this logic yourself:
class Service extends Component
{
private $_client = null;
public $clientClass;
public function getClient()
{
if (null !== $this->_client) {
return $this->_client;
}
$this->_client = new $clientClass;
return $this->_client;
}
}
Alternatively, you can register Goutte\Client as a separate component, then Yii will properly instantiate it.
UPDATE:
To clarify, instantiating objects from config is done with yii\base\Configurable interface which is implemented in yii\base\Object class. Eventually, this implementation executes Yii::configure:
public static function configure($object, $properties)
{
foreach ($properties as $name => $value) {
$object->$name = $value;
}
return $object;
}
As you see, all properties will be assigned their respective values, so _client will become an array, not an object.

Answer 2

Found another approach in the guide itself: The property targets of the class yii\log\Dispatcher can be initialized with a class names or an objects. To make it working as one expects the init method is overwritten:
/**
* {#inheritdoc}
*/
public function init()
{
parent::init();
foreach ($this->targets as $name => $target) {
if (!$target instanceof Target) {
$this->targets[$name] = Yii::createObject($target);
}
}
}
This allows configuration/initialization of the log component like this:
'log' => [
'class' => 'yii\log\Dispatcher',
'targets' => [
[
'class' => 'yii\log\FileTarget',
],
],
],
Note: targets is an array here. But it can be done with a single class/object as well.
So in your case this should be a solution:
namespace app\models;
class Scraper extends ActiveRecord // or extends from anything that actually implements yii\base\Configurable
{
public $_client;
/**
* {#inheritdoc}
*/
public function init()
{
parent::init();
if (!$this->_client instanceof Goutte\Client) {
$this->_client = Yii::createObject($this->_client);
}
}
}
btw: usually underscore prefix in variable names is used for private properties.