问题描述

我对 OOP 风格的 PHP 很陌生，我也在尝试实现 PDO.我在网上找到了这个处理数据库连接的不错的小类，但是我不知道如何从另一个类访问它.代码如下:

I am very new to OOP styled PHP, and I am trying to implement PDO as well. I found this nice little class online which handles the database connection, however I have no idea how to access it from another class. Here is the code:

  class PDO_DBConnect {
    static $db ;
    private $dbh ;
    private function PDO_DBConnect () {
        $db_type = 'mysql';  //ex) mysql, postgresql, oracle
        $db_name = 'postGal';
        $user = 'user' ;
        $password = 'pass' ;
        $host = 'localhost' ;
        try {
            $dsn = "$db_type:host=$host;dbname=$db_name";
            $this->dbh = new PDO ( $dsn, $user, $password);
            $this->dbh->setAttribute(PDO::ATTR_PERSISTENT, true);
            $this->dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        } catch ( PDOException $e ) {
            print "Error!: " . $e->getMessage () . "
" ;
            die () ;
        }
    }

    public static function getInstance (  ) {
        if (! isset ( PDO_DBConnect::$db )) {
            PDO_DBConnect::$db = new PDO_DBConnect ( ) ;
        }
        return PDO_DBConnect::$db->dbh;
    }
  }

  $db_handle = PDO_DBConnect::getInstance(); 

    class Person 
  {
    function __construct()
    {
      $STMT = $db_handle->prepare("SELECT title FROM posts WHERE id = ? AND author = ? LIMIT 20");
      $STMT->execute(array('24', 'Michael'));

      while ($result = $STMT->fetchObject()) 
      {
        echo $result->title;
        echo "<br />";
      }  
    }
  }

如何访问我的 Person 类中的 $db_handle 变量?我是否必须在 Person 类中实例化变量?如果是这样，那是否意味着我将始终必须将其称为 $this->db_handle ?我希望避免这种情况.(我对类的变量作用域仍然只有非常基本的了解)

How can I gain access to the $db_handle variable inside of my Person class? Do i have to instantiate the variable inside of the Person class? If so, does that mean I will always have to call it as $this->db_handle ? I was hoping to avoid that. (I still only have a very basic understanding of variable scope with classes)

推荐答案

有(至少)三种方法来处理这个问题.最便携且经常被推荐的方法称为依赖注入"，您可以通过它的 __construct() 将数据库句柄传递到您的类中，并将其存储在类变量中.需要使用 $this->db 访问它，就像您不想做的那样.

There are (at least) three ways to handle this. The most portable, and oft recommended is called "dependency injection", whereby you pass the database handle into your class via its __construct() and store it in a class variable. Requires accessing it with $this->db like you didn't want to have to do.

class Person {
  // Member to hold the db handle
  public $db;

  public function __construct($db_handle) {
    // Assign the handle to a class member variable in the constructor
    $this->db = $db_handle;
  }
  public function otherFunc() {
    $this->db; // do something
  }
}

$person = new Person($db_handle);

下一个方法是在构造函数中实例化 $db_handle 而不是将其传入.这有点难以测试和调试.

Next method would be to instantiate the $db_handle inside the constructor rather than passing it in. This is a little harder to test and debug.

class Person {
   public $db;
   public function __construct() {
      $this->db = PDO_DBConnect::getInstance();
   }
}

最后，您可以在课堂中使用 $db_handle 作为 global 调用它.这可能是最难阅读和调试的.

Finally, you can call $db_handle as a global whenever you use it in your class. This is perhaps the hardest to read and debug.

class Person {
  public function __construct() {
    global $db_handle;
  }
  public function otherFunc() {
    global $db_handle;
    $db_handle; // do something
  }
}

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