use database class in another class

Question

I have 2 class in my CMS and there are crud functions in "User Class". How can I use database class in another class. I know they both work. But I was previously transferring with the "extends" method. But every time I created an object, the database connection was duplicated. So "extends" was fault for me. I don't want to fault again.

So which is best solution? Do any of these solutions duplicate the database connection?

databaseclass.php:

class database
{
    public $connect;

    function __construct() {
        $this->connect();
    }
    public function connect() {
        $this->connect = new PDO('mysql:host=' . SERVER . ';dbname=' . DB_NAME . ';charset=utf8', DB_USER, DB_PASS);
    }
}

userclass.php:

class user
{

    function getUser() {
        # select an user codes
    }
}

1. Solution - Injection database class

   class user
   {
   
       function getUser($database) {
           $mysql_command = $database->connection->prepare('SELECT * FROM users WHERE id = 1');
           $mysql_command->execute();
           return $mysql_command->fetch(PDO::FETCH_ASSOC);
       }
   }
   

2. Solution - Global database class (I want that but everybody suggest first solution) (I want because this solution does not require me to inject each time I create a user object) userclass.php:

   class user
   {
   
       function getUser() {
           global $database;
           $mysql_command = $database->connection->prepare('SELECT * FROM users WHERE id = 1');
           $mysql_command->execute();
           return $mysql_command->fetch(PDO::FETCH_ASSOC);
       }
   }
   

Answer 1

I added a third option here and gave some personal opinion about the others:

Solution a) Pass as parameter to your methods

This way you always need to pass it inside your functions which makes the API of your class less clean. Imagine we want to get a user by id. This could look like: getUserById($database, 123). This will require everywhere to know how to fetch the databse. I would try to avoid this.

Solution b) Use it as global

I would try avoid global wherever I can. My first argument would be that it makes your class less testable and can change the behaviour dependent on the context. Here is a nice post about it with more examples: https://stackoverflow.com/a/5166527/12880865

Solution c) Use dependency injection with the __constructor.

I would add another way of solving it by using dependency injection at constructor level already. This way you can use getUsers() or getUserById($id) without passing the database all the time. This way your class defines it's own dependencies very clearly for the user of this class.

this solution does not require me to inject each time I create a user object

To avoid this you could use container which could resolves your class dependencies automatically when you try to retrieve them.

Example with your code:

class user
{
    protected $database;

    public function __construct(database $database) {
        $this->database = $database;
    }

    function all() {
        # select an user codes
        $this->database->query('....');
    }

    function getById($id) {
        # select an user codes
        $this->database->query('....', ['id' => $id]);
    }
}

which you can then inject like this:

$database = new Database();

// Here you'll pass your database connection into the repository
$users = new UserRepository($database); 
$users->all(); // returns an array of all users
$users->getById(123); // returns a specific user by id

// Here you'll pass the same database connection into another repository
$posts = new PostRepository($database);
$posts->all(); // returns an array of all posts
$posts->getById(123); // returns a specific post by id