在php中正确地使用其他类中的类？ [英] Properly using classes in other classes in php?

问题描述

很久以前应该问过某人。

在其他课程中使用其他课程的最佳方法是什么？

例如，假设我有一个应用程序类：

 类应用程序
 {
 public function displayVar（）{
 echo'hello world'; 
} 
} 
  

和数据库类

类数据库
{
//连接到db on construct
public function query（）{
/ / queries db
}
}


现在，我想添加一个函数我的应用程序类使用db类中的函数

 类应用程序
 {
 public function displayVar （）{
 echo'hello world'; 
} 
 public function getVar（）{
 global $ db; 
 $ sql = foo; 
 $ db-> query（$ sql）; 
} 
} 
  

所以我有

  $ db = new Database（）; 
 $ app = new Application（）; 
 $ app-> getVar（'var'）; 
  

有更好的方法吗？

解决方案

有一对夫妇的做法的方式。全局变量当然是一种方式，也最看不起。您可以创建 Singleton 和所有需要数据库访问的其他类调用此单例。

  final类数据库{
 private static $ connection; 
 
 public static function getInstance（）{
 if（self :: $ connection == NULL）{
 self :: $ connection = //你的数据库连接
} 
 return self :: $ connection; 
} 
} 
  

并使用此数据库连接对象在任何类需要它。

 类应用程序{
 public function displayVar（）{
 echo'hello world'; 
} 
 public function getVar（）{
 $ db = Database :: getInstance（）; 
 $ sql = foo; 
 $ db-> query（$ sql）; 
} 
} 
  

这是一个很好的开始和伟大的一步超越使用全局变量，但您可以通过依赖注入做得更好。依赖注入是一个简单的概念，如果一个类有任何外部依赖，例如你的示例中的数据库连接，你显式地传递给needy类在其构造函数或方法。所以新的代码看起来像Jonathan的解决方案。使用依赖注入的一个主要优点是在单元测试中，你可以很容易地用一个mock对象替换这个实际的数据库对象，并将它传递给任何需要它的人。

  class Application {
 private $ db; 
 
 public function __construct（Database $ db）{
 $ this-> db = $ db; 
} 
 
 public function displayVar（）{
 echo'hello world'; 
} 
 
 public function getVar（）{
 $ sql = foo; 
 $ this-> db-> query（$ sql）; 
} 
} 
  

对于较小的项目，您可以自己轻松地做。对于大型项目，有各种 DI框架可用于PHP < a>

Should have asked someone this a long time ago.

What is the best way to use other classes within another class?

For instance, lets say I have an application class:

class Application
{
    public function displayVar() {
        echo 'hello world';
    }
}

and a database class

class Database
{
    // connects to db on construct
    public function query() {
        // queries db
    }
}

now, i want to add a function to my application class that uses a function from the db class

class Application
{
    public function displayVar() {
        echo 'hello world';
    }
    public function getVar() {
        global $db;
        $sql = foo;
        $db->query($sql);
    }
}

so then I have

$db = new Database();
$app = new Application();
$app->getVar('var');

Is there a better way of doing this? Really what I am looking for is the standard way of doing it, not another way of rigging it.

解决方案

There are a couple of ways of doing that. Global variables is certainly one way and the most looked down upon too. You can create a Singleton and all other classes that need database access would call upon this singleton.

final class Database {
    private static $connection;

    public static function getInstance() {
        if(self::$connection == NULL) {
            self::$connection = // init your database connection
        }
        return self::$connection;
    }
}

And use this database connection object in whatever class needs it.

class Application {
    public function displayVar() {
        echo 'hello world';
    }
    public function getVar() {
        $db = Database::getInstance();
        $sql = foo;
        $db->query($sql);
    }
}

This is all well for a start and a great step beyond using global variables, but you can do better with Dependency Injection. Dependency Injection is a simple concept that if a class has any external dependencies, such as the database connection in your example, you explicitly pass those to the needy class in its constructor or a method. So the new code would look something like Jonathan's solution. A major advantage of using dependency injection is in unit testing, where you can easily replace this actual database object with a mock object and pass it to whoever needs it.

class Application {
    private $db;

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

    public function displayVar() {
        echo 'hello world';
    }

    public function getVar() {
        $sql = foo;
        $this->db->query($sql);
    }
}

For smaller projects, you can easily do it yourself. For large projects, there are various DI frameworks available for PHP

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