How to set up and inject multiple PDO database connections in slim 4?

Question

I could make an instance of PDO and inject it successfully. I defined the PDO::class directly and injected it in the constructor with __const

Answer 1

You have multiple options:

1. Extending PDO
2. Autowired objects

1. Extending PDO

use PDO;

class PDO2 extends PDO
{
    // must be empty
}

The container definition:

use PDO2;

// ...

return [
    PDO::class => function (ContainerInterface $container) {
        return new PDO(...);
    },

    PDO2::class => function (ContainerInterface $container) {
        return new PDO2(...);
    },
];

Usage

use PDO;
use PDO2;

class MyRepository
{
    private $pdo;

    private $pdo2;
    
    public function __construct(PDO $pdo, PDO2 $pdo2)
    {
        $this->pdo = $pdo;
        $this->pdo2 = $pdo2;
    }
}

2. Autowired objects

See Matthieu Napoli's answer: https://stackoverflow.com/a/57758106/1461181

Answer 2

If you have multiple instances of a class in your app (here you have multiple instances of the PDO class), then you must configure which one to inject every time.

That means that PDO cannot be autowired, because PHP-DI cannot decide which instance you want depending on the service/controller/etc.

You need to use configuration (see http://php-di.org/doc/php-definitions.html#autowired-objects) to define which instance (db1 or db2 in your example) to inject for each service.

return [
    MyService::class => DI\autowire()
        ->constructorParameter('pdo', DI\get('db1'))
        ->constructorParameter('pdo2', DI\get('db2')),

    'db1' => function (ContainerInterface $c) {
        return new PDO();
    },
    'db2' => function (ContainerInterface $c) {
        return new PDO();
    },
];