Sharing dependancies in Symfony services without passing parameters to sub classes - php

Question

A lot of my services rely on a PDO connection to an external database (for reasons specific to my application, it made sense to use this strategy over using Doctrine). To start a PDO connection, each services needs a data source name, username and password. This leaves my services.yml containing much of the same arguments for each service:
#AppBundle\Resources\config\services.yml
# ...
QueryDataBuilderHelper:
class: AppBundle\Services\QueryDataBuilderHelper
arguments: [ "%database_host%", "%database_user%", "%database_password%" ]
ZipCodeClass:
class: AppBundle\Services\ZipCodeClass
arguments: [ "%database_host%", "%database_user%", "%database_password%" ]
# ...
Is it possible to define the connection somewhere and reference it in all services without passing parameters to each one?
The Symfony cookbook recommends using parent services and extending the parent services. When I try to use the subclass, the subclass doesn't pull the arguments of the superclass:
#AppBundle\Resources\config\services.yml
DBConnectionHelper:
class: AppBundle\Services\DBConnectionHelper
arguments: [ "%database_host%", "%database_user%", "%database_password%" ]
DBSubClass:
class: AppBundle\Services\DBSubClass
parent: DBConnectionHelper
arguments: [ "%unrelated_parameter%" ]
//AppBundle\Services\SuperClassService.php
namespace AppBundle\Services;
class DBConnectionHelper
{
public function __construct($dsn, $user, $password){
$this->DB_connection = new \PDO($dsn, $user, $password);
}
}
//AppBundle\Services\DBSubClass.php
namespace AppBundle\Services;
class DBSubClass extends DBConnectionHelper
{
public function __construct($unrelated_param){
//Calling parent::__construct() here will require the parameters again.
//Which is what I am trying to avoid...
// Outputs a notice that DB_Connection isn't set.
var_dump($this->DB_Connection());
$this->unrelated_param = $unrelated_param;
}
}
I've used the constructor here instead of setters because these dependancies are not optional. The Symfony docs suggest that setters should only be used when dependancies are optional.

Answer 1

What you need to use here is called an Abstract Service. Luckily for you, Symfony is providing a way to achieve this. The options you're looking for are abstract and parent. You can read the entire chapter here.
I will try to briefly explain the example from documentation, so that you can grasp the idea.
# ...
services:
# ...
mail_manager:
abstract: true
calls:
- [setMailer, ["#my_mailer"]]
- [setEmailFormatter, ["#my_email_formatter"]]
newsletter_manager:
class: "NewsletterManager"
parent: mail_manager
greeting_card_manager:
class: "GreetingCardManager"
parent: mail_manager
Basically what you need to do is this:
Create an abstract class where you will define all common properties/methods.
Then configure these common method calls in your service file accordingly and add the option abstract. Since your service is an abstract one it means that it cannot be instantiated, so class option here is omitted.
After that create a service like you always do, and don't forget to extend the abstract class. Then register that service in your service.yml file and add the parent option to it, by setting the name of your abstract service.
Repeat the step above as many times as you wish for each child service and you should be good to go.
If you have any questions, leave a comment. Hope this can help you out.

Answer 2

Rather than extend your DBConnectionHelper class, you could inject it as a dependancy via your constructor.
//AppBundle\Services\DBSubClass.php
namespace AppBundle\Services;
class DBSubClass
{
private $dbConnectionHelper;
public function __construct($dbConnectionHelper, $unrelated_param)
{
$this->dbConnectionHelper = $dbConnectionHelper;
$this->unrelated_param = $unrelated_param;
}
}
You can then get your connection using $this->dbConnectionHelper->DB_Connection().
You would also need to configure your service as:
DBSubClass:
class: AppBundle\Services\DBSubClass
arguments: [ "#DBConnectionHelper", "%unrelated_parameter%" ]