Question

我有点问题。我有一个名为BaseModel的类。有一个pdo连接。现在我有一个名为TestModel的其他类，我扩展了BaseModel类。但是当我在pdo变量上创建一个var_dump（）时，它返回null。我知道它的问题因为构造函数，但我该怎么做呢？我需要TestModel中的构造函数。但是whitout constcuter变量返回null。我已经尝试过白色parent::__construct()，但页面加载无限。

这是我的课程

BaseModel

<?php

namespace App\System\MVC\Models;

class BaseModel
{
  protected $config;
  protected $connection;

  public function __construct($config, $connection)
  {
    $this->config     = $config;
    $this->connection = $connection;
  }

  public function __destruct()
  {
    $this->config     = null;
    $this->connection = null;
  }
}

?>

TestModel

<?php

namespace App\System\MVC\Models;

use App\System\MVC\Models\BaseModel;

class TestModel extends BaseModel
{
  protected $config;
  protected $connection;

  public function __construct()
  {
    var_dump($this->connection);
  }

  public function __destruct()
  {
    $this->config     = null;
    $this->connection = null;
  }
}

?>

请帮帮我。感谢

抱歉英文不好。

Answer 1

您永远不会将所需的变量传递给子类实例，因此您无法获得任何其他结果。对于初学者，使用正确的参数调用超级构造函数：

class TestModel extends BaseModel
{
    // no need to redeclare the properties

    public function __construct($config, $connection)
    {
        // pass the variables to __construct() in BaseModel
        parent::__construct($config, $connection);
        // some other initialization
    }

    // no need for destructor since the parent one is called
}

现在您可以像这样使用您的模型：

$obj = new TestModel($config, $connection);
var_dump($obj->getAllChildren()); // whatever operations that you want

但是每次使用模型时都必须传递$config和$connection，这是一种痛苦，因为你可以肯定。在这种情况下，您可能想要某种factory。你能做的最简单的就是这样：

class ModelFactory
{
    const NS = 'App\System\MVC\Models';
    private $config;
    private $connection;

    public function __construct($config, $connection)
    {
        $this->config = $config;
        $this->connection = $connection;
    }

    public function create($class_name)
    {
        $reflection = new ReflectionClass(self::NS . '\\' . $class_name);
        return $reflection->newInstance($this->config, $this->connection);
    }
}

这将只允许您指定一次参数，然后您可以非常轻松地创建任意数量的模型实例：

$factory = new ModelFactory($config, $connection);
$obj1 = $factory->create('UserModel'); // creates new App\System\MVC\Models\UserModel
$obj2 = $factory->create('GroupModel'); // creates new App\System\MVC\Models\GroupModel

这应该会让事情变得容易一些。请记住，通常模型没有连接，它们只有（元）数据，然后另一个对象负责执行查询。看看repository and data access object patterns。

Answer 2

在实例化子类时，不会自动调用父构造函数，而在您的情况下，无法为父构造函数提供依赖项，因为它们未提供给子构造函数。

你的课程应该像这样重新实现：

<?php

namespace App\System\MVC\Models;

class BaseModel
{
  protected $config;
  protected $connection;

  public function __construct($config, $connection)
  {
    $this->config     = $config;
    $this->connection = $connection;
  }

  public function __destruct()
  {
    $this->config     = null;
    $this->connection = null;
  }
}

?>

<?php

namespace App\System\MVC\Models;

use App\System\MVC\Models\BaseModel;

class TestModel extends BaseModel
{
  /* You don't need to redefine them as they are inherited from the parent  
  protected $config;
  protected $connection;
  */

  public function __construct($config, $connection)
  {

    parent::__construct($config, $connection);
    var_dump($this->connection);
  }
  /* This is also inherited from the parent 
  public function __destruct()
  {
    $this->config     = null;
    $this->connection = null;
  }
  */
}

?>

变量在扩展类后返回null

2 个答案: