PHP - Extending Class | 易学教程

问题

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.

I am trying to access a method in a parent class, but you can see the issue.

Parent class:

 class DatabaseObject { 

     public static function find_all() {
        return self::find_by_sql("SELECT * FROM " . self::$table_name);
    }
}

Child Class:

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:

$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.

回答1:

You could try late static binding as mentioned below, or a singleton solution should work as well:

<?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2:

You should look into the concept of Late Static Binding in PHP. This allows you to access a static constant or function from the class that was called.

来源：https://stackoverflow.com/questions/11194506/php-extending-class

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