如何创建2个PDO数据库连接实例PHP

Question

I currently have a class which creates one database connection, however I would like to create another connection too. I have tried copying the class structure but just renaming the variables and functions however that doesn't work and it seems like it doesn't detect where my new PDO connection is as I get error Uncaught Error: Call to a member function prepare() on null in . What is the best approach to take in my case when creating 2 database connections?

config.php:

<?php

class Database
{   
    private $host = "localhost";
    private $db_name = "database1";
    private $username = "root";
    private $password = "";
    public $conn;

    public function dbConnection()
    {

        $this->conn = null;    
        try
        {
            $this->conn = new PDO("mysql:host=" . $this->host . ";dbname=" . $this->db_name, $this->username, $this->password);
            $this->conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);   
        }
        catch(PDOException $exception)
        {
            echo "Connection error: " . $exception->getMessage();
        }

        return $this->conn;
    }
}

?>

class.user.php:

class USER
{   

    private $conn;

    public function __construct()
    {
        $database = new Database();
        $db = $database->dbConnection();
        $this->conn = $db;
    }

    public function runQuery($sql)
    {
        $stmt = $this->conn->prepare($sql);
        return $stmt;
    }
}

Answer 1

You could create your User class and pass the connection to the constructor. This will give you flexibility to swap out the connection.

Regarding your database class, it seems to be a wrapper, to create a PDO connection. You could do away with it, or extend the class with different params.

Perhaps look at dependency injection, and containers. They might help you here.

<?php  
class User
{   

    private $conn;

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

    public function runQuery($sql)
    {
        $stmt = $this->conn->prepare($sql);

        return $stmt;
    }
}