Definition and Usage of Dependency Injection in PHP Classical Design Pattern

This paper illustrates the definition and usage of dependency injection in PHP classic design pattern. Share it for your reference, as follows:

The essence of dependency injection is to separate the impossible and replaceable parts of a class, and use them by injection, so as to achieve the purpose of decoupling.

1 database connection class:

class Mysql{
 private $host;
 private $prot;
 private $username;
 private $password;
 private $db_name;
 //  Construction method 
 public function __construct(){
   $this->host = '127.0.0.1';
   $this->port = 22;
   $this->username = 'root';
   $this->password = '';
   $this->db_name = 'my_db';
 }
 //  Connect 
 public function connect(){
   return mysqli_connect($this->host,$this->username,$this->password,$this->db_name,$this->port);
 }
}

Use this class:

$db = new Mysql();
$db->connect();

Usually, the database connection class should be designed as a single column, so don't make it complicated here.

Dependency injection

Obviously, the configuration of the database is a replaceable part, so we need to carry it out first:

class MysqlConfiguration{
  private $host;
  private $prot;
  private $username;
  private $password;
  private $db_name;
  public function __construct($host,$port,$username,$password,$db_name){
    $this->host = $host;
    $this->port = $port;
    $this->username = $username;
    $this->password = $password;
    $this->db_name = $db_name;
  }
  public function getHost(){
    return $this->host;
  }
  public function getPort(){
    return $this->port();
  }
  public function getUsername(){
    return $this->username;
  }
  public function getPassword(){
    return $this->password;
  }
  public function getDbName(){
    return $this->db_name;
  }
}

Then the irreplaceable part is like this:

class Mysql{
 private $configuration;
 public function __construct($config){
   $this->configuration = $config;
 }
 //  Connect 
 public function connect(){
   return mysqli_connect($this->configuration->getHost(),$this->configuration->getUsername(),$this->configuration->getPassword(),$this->configuration->getDbName(),$this->configuration->getPort());
 }
}

This completes the separation of configuration files and connection logic.

Use

$config = new MysqlConfiguration('127.0.0.1','root','password','my_db',22);
// $config Is injected Mysql This is called dependency injection 
$db = new Mysql($config);
$db->connect();

More readers interested in PHP can check out the topics on this site: "Introduction to php Object-Oriented Programming", "Encyclopedia of PHP Array (Array) Operation Skills", "Introduction to PHP Basic Syntax", "Summary of PHP Operation and Operator Usage", "Summary of php String (string) Usage", "Introduction to php+mysql Database Operation" and "Summary of php Common Database Operation Skills"

I hope this article is helpful to everyone's PHP programming.