如何在php中编写数据库连接mysqli的依赖注入？

Question

I have tried to write to write the dependency injection but the class file is getting an error. How to properly write the database connection class and use it as a dependency injection?. Please check with the following error. How to write the connection once and call it everywhere in php files.

Database.php

class Database
{
    private $host ="localhost";
    private $user = "root";
    private $password="xxxx";
    private $db="";
    private $mysqli;


    function __construct($host,$user,$pass,$data) {

        $this->host     = $host;
        $this->user     = $user;
        $this->pass     = $pass;
        $this->data     = $data;
        $this->mysqli   = new mysqli($this->host, $this->user, $this->pass, $this->data);
    }

    public function query($query)
    {
        return $this->mysqli->query($query);
    }
}

Dummy.php

require_once("../apitest/database.php");

class Dummy
{
    protected $db;

    function __construct(Database $db)
    {
        $this->db = $db;
    }

    function get_test_yada(){
        return $this->db->mysqli->query("SELECT test FROM test")->fetch_object()->test;
    }
}

Code:

$test = new Dummy();
echo $test->get_test_yada();

Error

PHP Fatal error: Uncaught TypeError: Argument 1 passed to Dummy::__construct() must be an instance of Database, none given, called in /var/www/html/apitest/index.php on line 19 and defined in /var/www/html/apitest/index.php:8 Stack trace: #0 /var/www/html/apitest/index.php(19): Dummy->__construct() #1 {main} thrown in /var/www/html/apitest/index.php on line 8

Answer 1

You're not passing Database instance when you're trying to instantiate Dummy object.

It should look like this:

<?php

$host = 'localhost';
$user = 'root';
$pass = '';
$dbname = 'db';

$db = new Database($host,$user,$pass,$dbname);
$test = new Dummy($db);
echo $test->get_test_yada();