PHP design pattern-detailed explanation of the use of dependency injection-PHP Tutorial-php.cn

PHP design pattern-detailed explanation of the use of dependency injection

黄舟

Release： 2023-03-14 09:54:02

Original

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Preface

Finally let’s talk about this famous Design Principle. In fact, it is simpler than other Design Patterns.
The essence of dependency injection is to separate the irreplaceable parts of a class from the replaceable parts and use them through injection to achieve the purpose of decoupling.

Here is an example of a database link. I hope everyone understands that

A database connection class

class Mysql{
    private $host;
    private $port;
    private $username;
    private $password;
    private $db_name;
    public function construct(){
        $this->host = &#39;127.0.0.1&#39;;
        $this->port = 22;
        $this->username = &#39;root&#39;;
        $this->password = &#39;&#39;;
        $this->db_name = &#39;my_db&#39;;
    }
    public function connect(){
        return mysqli_connect($this->host,$this->username ,$this->password,$this->db_name,$this->port); 
    }
}

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Used

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

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should usually be designed as a singleton. Let’s not get too complicated here.

Dependency Injection

Obviously, the database configuration is a replaceable part, so we need to take it out.

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

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Then the irreplaceable part is like this:

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

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This completes the separation of configuration file and connection logic.

Using

$config = new MysqlConfiguration(&#39;127.0.0.1&#39;,&#39;root&#39;,&#39;&#39;,&#39;my_db&#39;,22);
$db = new Mysql($config);
$con = $db->connect();

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$config is injected into Mysql, which is called dependency injection.

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