PHP - 扩展类
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PHP - Extending Class
提问by TheLettuceMaster
I've done lots and lots of code in PHP that is object-oriented, but up until now, all of my classes have been, "singular", I suppose you can call it. I am in the process of changing several classes (that have 5 or so identical methods) to extend one class (to rid myself of duplicate code). I am running into a few issues.
我已经用 PHP 编写了很多面向对象的代码，但到目前为止，我所有的类都是“单一的”，我想你可以称之为。我正在更改几个类（有 5 个左右相同的方法）以扩展一个类（以消除重复的代码）。我遇到了一些问题。
I am trying to access a method in a parent class, but you can see the issue.
我正在尝试访问父类中的方法，但您可以看到问题。
Parent class:
父类：
class DatabaseObject {
public static function find_all() {
return self::find_by_sql("SELECT * FROM " . self::$table_name);
}
}
Child Class:
儿童班：
class Topics extends DatabaseObject {
protected static $table_name = "master_cat";
protected static $db_fields = array('cat_id', 'category');
public $cat_id;
public $category;
}
Code trying to access all info from this table from php/html file:
尝试从 php/html 文件访问此表中所有信息的代码：
$topics=Topics::find_all();
foreach($topics as $topic):
echo $topic->category;
endforeach;
As you can see, Most of the code has not been merged to the new way of doing things. I need to change the self::$table_name which no longer works in the new way I am doing things. I will have about 5 Classes extending this object, so what is the best way of coding this so I can access different tables with one method (rather than including this exact find_all() method in 5 different classes.
如您所见，大部分代码尚未合并到新的处事方式中。我需要更改 self::$table_name ，它不再以我做事的新方式工作。我将有大约 5 个类扩展这个对象，那么什么是最好的编码方式，这样我就可以用一种方法访问不同的表（而不是在 5 个不同的类中包含这个确切的 find_all() 方法。
回答by Matthijs
You could try late static binding as mentioned below, or a singleton solution should work as well:
您可以尝试如下所述的后期静态绑定，或者单例解决方案也应该有效：
<?php
abstract class DatabaseObject {
private $table;
private $fields;
protected function __construct($table, $fields) {
$this->table = $table;
$this->fields = $fields;
}
public function find_all() {
return $this->find_by_sql('SELECT * FROM ' . $this->table);
}
}
class Topics extends DatabaseObject {
private static $instance;
public static function get_instance() {
if (!isset(self::$instance)) {
self::$instance = new Topics('master_cat', array('cat_id', 'category'));
}
return self::$instance;
}
}
Topics::get_instance()->find_all();
回答by Jeremy Livingston
You should look into the concept of Late Static Bindingin PHP. This allows you to access a static constant or function from the class that was called.
您应该研究PHP中后期静态绑定的概念。这允许您从被调用的类访问静态常量或函数。
