(Notes:<\/p>\n
)<\/p>\n
I have one thing to say for all of those PHP developers who look at Rails’ ActiveRecord class and get all excited about implementing it in PHP:<\/p>\n
It can’t be done.\u00a0 Yet.<\/p>\n
Here’s why:<\/p>\n
Until PHP5.3, PHP does not implement a feature called “late static binding”.\u00a0 What is late static binding?\u00a0 Well, how about I show you what it’s like to NOT have late static binding:<\/p>\n
class A {\r\n public static function who() {\r\n echo __CLASS__;\r\n }\r\n public static function test() {\r\n self::who();\r\n }\r\n}\r\nclass B extends A {\r\n public static function who() {\r\n echo __CLASS__;\r\n }\r\n}\r\nB::test(); \/\/Outputs: 'A'<\/pre>\nThat’s right:\u00a0 B::test() outputs ‘A’.\u00a0 This is a problem, because while it is true that B is a subclass of A, B is still B.\u00a0 When I call a static method of B, I want it to know that it’s B.<\/p>\n
With late static binding (only available in PHp5.3 and onward), this goes away:<\/p>\n
<?php\r\nclass A {\r\n public static function who() {\r\n echo __CLASS__;\r\n }\r\n public static function test() {\r\n static::who(); \/\/ Here comes Late Static Bindings\r\n }\r\n}\r\nclass B extends A {\r\n public static function who() {\r\n echo __CLASS__;\r\n }\r\n}\r\nB::test(); \/\/Outputs 'B'\r\n?><\/pre>\nWhy is this a problem for ActiveRecord?\u00a0 Well, say we define a class called ActiveRecord, and create a subclass of ActiveRecord called Person.\u00a0 When I call Person::find_all(), PHP5.2 is going to run find_all in ActiveRecord – and ActiveRecord’s find_all() will not know what kind of subclass I am.\u00a0 It won’t know if I’m a Person, Dog, Pizza, or any of that jazz.\u00a0 Essentially, ActiveRecord is now dead in the water.<\/p>\n
Now, you could just make find_all a standard method instead of a static one, but then for every find operation, you’d have to do this:<\/p>\n
$p = new Person();\r\n$persons = $p->find_all();<\/pre>\nSemantically, this doesn’t make much sense.<\/p>\n
But, PHP coders, take heart –\u00a0 there are two silver linings:<\/em><\/p>\n