How to practically use the Observer pattern in laravel?

问题

So I am learning about design patterns and I am currently studying the Observer pattern.

To implement it on a raw basis, I did something like this:

<?php

class Subject
{
    private $foo;
    private $bar;

    private $observers = [];

    public function addObserver(Observer $o)
    {
        $this->observers[] = $o;
    }

    public function removeObserver(Observer $o)
    {
        if(($key = array_search($o, $this->observers, $TRUE)) !== FALSE) {
            unset($this->observers[$key]);
        }
    }

    public function notify()
    {
        foreach ($this->observers as $observer) {
            $observer->update($this->foo, $this->bar);
        }
    }

    public function setFoo($foo)
    {
        $this->foo = $foo;
    }

    public function setBar($bar)
    {
        $this->bar = $bar;
    }
}

interface Observer{
    function update($foo, $bar);
}

class Observer1 implements Observer
{
    private $foo;
    private $bar;

    public function update($foo, $bar){
        $this->foo = $foo;
        $this->bar = $bar;
    }

    public function display()
    {
        echo "Observer1 : Foo -> " . $this->foo . " Bar -> " . $this->bar . "\n";
    }
}

class Observer2 implements Observer
{
    private $foo;
    private $bar;

    public function update($foo, $bar){
        $this->foo = $foo;
        $this->bar = $bar;
    }

    public function display()
    {
        echo "Observer2 : Foo -> " . $this->foo . " Bar -> " . $this->bar . "\n";
    }
}

$subject = new Subject;


$observer1 = new Observer1;
$observer2 = new Observer2;

$subject->addObserver($observer1);
$subject->addObserver($observer2);

$subject->setFoo(5);
$subject->setBar(10);
$subject->notify();

$observer1->display();
$observer2->display();

$subject->setFoo(20);
$subject->setBar(40);
$subject->notify();

$observer1->display();
$observer2->display();

So I see that the observers are getting updated. Is this the correct way to implement the observer pattern? I guess I could abstract the functionality in the Subject to add, remove and notify into its own abstract class. I could also user the SplSubject and SplObserver that PHP provides. What else can be done here to make this code better?

But what I really want to know is where is the Observer pattern used in Laravel. It must be in use somewhere in the framework and I can learn from it. Secondly, what are the practical applications for this? One of the things that I could think of is when I am doing caching in laravel and a model gets updated, it might need to notify the cache objects to change. Is this a good practical application of the pattern? What others are there?

回答1:

In my project I used Observers to check if A model has changed and throw event if changes have been made.

Let say I have Observer for my User Model hence UserObserver. What the observer does is it checks for changes in my user. And if there is changes.

I have a event handler to save transactions.

E.g "John Doe has updated his first name from Mike to John"

Where first name is a field in my User Model named first_name; There is more to observers and one is my application.

来源：https://stackoverflow.com/questions/39267139/how-to-practically-use-the-observer-pattern-in-laravel

标签

php

laravel

observer-pattern